Question:* Which of the following is true about setTimeOut()?
Answer: • The statement(s) it executes run(s) only once.
Question:* How can the operating system of the client machine be detected?
Answer: • Using the navigator object
Question:* Which of the following prints "AbBc"?
Answer: • var b = 'a';
var result = b.toUpperCase() + 'b' + 'b'.toUpperCase() +'C'['toLowerCase']();
alert(result);
Question:* Which of the following descriptions is true for the code below?
var object0 = {};
Object.defineProperty(object0, "prop0", { value : 1, enumerable:false, configurable : true });
Object.defineProperty(object0, "prop1", { value : 2, enumerable:true, configurable : false });
Object.defineProperty(object0, "prop2", { value : 3 });
object0.prop3 = 4;
Answer: • Object 'object0' contains 4 properties. Property 'prop1' and property 'prop3' are available in the for...in loop. Property 'prop0' and property 'prop3' are available to delete.
Question:* Performance-wise, which is the fastest way of repeating a string in JavaScript?
Answer: • String.prototype.repeat = function(count) {
if (count < 1) return '';
var result = '', pattern = this.valueOf();
while (count > 0) {
if (count & 1) result += pattern;
count >>= 1, pattern += pattern;
}
return result;
};
Question:* Consider the following variable declarations:
var a="adam"
var b="eve"
Which of the following would return the sentence "adam and eve"?
Answer: • a.concat(" and ", b)
Question:* Which of the following code snippets will correctly split "str"?
Answer: • <script>
var str = 'something -- something_else';
var substrn = str.split(' -- ');
</script>
Question:* Which object can be used to ascertain the protocol of the current URL?
Answer: • location
Question:* Which of the following best describes a "for" loop?
Answer: • "for" loop consists of three optional expressions, enclosed in parentheses and separated by semicolons, followed by a statement executed in the loop.
Question:* Which of the following descriptions best describes the code below?
<script>
var variable1 = { fastFood: "spaghetti", length: 10 };
Object.freeze(variable1);
variable1.price = 50;
delete variable1.length;
</script>
Answer: • Object is frozen, a property named "price" is not added in the variable1 object, a property named "length" is not deleted from this object. At the end of the code, object "variable1" contains 2 properties.
Question:* Which of the following is not a valid HTML event?
Answer: • onblink
Question:* Analyze the following code snippet which uses a Javascript Regular Expression character set. What will be the output of this code?
<html>
<body>
<script type="text/javascript">
var str = "Is this enough?";
var patt1 = new RegExp("[^A-J]");
var result = str.match(patt1);
document.write(result);
</script>
</body>
</html
Answer: • s
Question:* Consider the following image definition:
<img id="logo" src="companylogo1.gif" height="12" width="12" >
Which of the following will change the image to companylogo2.gif when the page loads?
Answer: • document.getElementById('logo').src="companylogo2.gif"
Question:* What is the final value of the variable bar in the following code?
var foo = 9;
bar = 5;
(function() {
var foo = 2;
bar= 1;
}())
bar = bar + foo;
Answer: • 10
Question:* Which of the following are JavaScript unit testing tools?
Answer: • Buster.js, YUI Yeti, Jasmine
Question:* Which of the following can be used for disabling the right click event in Internet Explorer?
Answer: • event.button == 2
Question:* An image tag is defined as follows:
<img id="ERImage" width="100" height="100" onmouseover="ImageChange()" src="Image1.jpg">
The purpose of the ImageChange() function is to change the image source to Image2.jpg. Which of the following should the ImageChange() function look like?
Answer: • document.getElementById('ERImage').src="Image2.jpg"
Question:* Consider the following JavaScript alert:
<script type="text/JavaScript">
function message() {
alert("Welcome to ExpertRating!!!")
}
</script>
Which of the following will run the function when a user opens the page?
Answer: • body onload="message()"
Question:* Which of the following code snippets will correctly get the length of an object?
Answer: • <script>
var newObj = new Object();
newObj["firstname"] = "FirstName";
newObj["lastname"] = "LastName";
newObj["age"] = 21;
Object.size = function(obj) {
var size = 0, key;
for (key in obj) {
if (obj.hasOwnProperty(key)) size++;
}
return size;
};
var size = Object.size(newObj);
</script>
Question:* Which of the following Array methods in JavaScript runs a function on every item in the Array and collects the result from previous calls, but in reverse?
Answer: • reduceRight()
Question:* In an HTML page, the form tag is defined as follows:
<form onsubmit="return Validate()" action="http://www.mysite.com/">
The validate() function is intended to prevent the form from being submitted if the name field in the form is empty. What should the validate() function look like?
Answer: • <script type="text/javascript">
function Validate() {
if(document.forms[0].name.value == "")
return false;
else
return true;
}
</script>
Question:* Which of the following code snippets changes an image on the page?
Answer: • var img = document.getElementById("imageId");
img.src = "newImage.gif";
Question:* Which of the following results is returned by the JavaScript operator "typeof" for the keyword "null"?
Answer: • object
Question:* What will be the final value of the variable "apt"?
var apt=2;
apt=apt<<2;
Answer: • 8
Question:* How can a JavaScript object be printed?
Answer: • console.log(obj)
Question:* Which of the following is the correct syntax for using the JavaScript exec() object method?
Answer: • RegExpObject.exec(string)
Question:* Having an array object var arr = new Array(), what is the best way to add a new item to the end of an array?
Answer: • arr.push("New Item")
Question:* Consider the following JavaScript validation function:
function ValidateField()
{
if(document.forms[0].txtId.value =="")
{return false;}
return true;
}
Which of the following options will call the function as soon as the user leaves the field?
Answer: • input name=txtId type="text" onblur="return ValidateField()"
Question:* Which of following uses the "with" statement in JavaScript correctly?
Answer: • with (document.getElementById("blah").style) {
background = "black";
color = "blue";
border = "1px solid green";
}
Question:* Consider the following JavaScript validation function:
<script type="text/JavaScript">
function ValidateField()
{
if(document.forms[0].txtId.value =="")
{return false;}
return true;
}
</script>
Which of the following options will call the function as soon as the user leaves the field?
Answer: • input name=txtId type="text" onblur="return ValidateField()"
Question:* Which of the following modifiers must be set if the JavaScript lastIndex object property was used during pattern matching?
Answer: • g
Question:* Consider the following image definition:
<img id="logo" src="companylogo1.gif" height="12" width="12" >
Which of the following will change the image to "companylogo2.gif" when the page loads?
Answer: • document.getElementById('logo').src="companylogo2.gif"
Question:* Which of the following will check whether the variable vRast exists or not?
Answer: • if (typeof vRast =="undefined") {}
Question:* What would be the use of the following code?
function validate(field) {
var valid=''ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'';
var ok=''yes'';
var temp;
for(var i=0;i<field.value.length;i++) {
temp='''' + field.value.substring(i,i+1)
if(valid.indexOf(temp)==''-1'') {
ok=''no'';
}
}
if(ok==''no'') {
alert(''error'');
field.focus();
}
}
Answer: • It will force a user to enter only English alphabet character values.
Question:* An image tag is defined as follows:
<img id="ERImage" width="100" height="100" onmouseover="ImageChange()" src="Image1.jpg">
The purpose of the ImageChange() function is to change the image source to "Image2.jpg". Which of the following should the ImageChange() function look like?
Answer: • document.getElementById('ERImage').src="Image2.jpg"
Question:* Which of the following choices will detect if "variableName" declares a function?
<script>
var variableName= function(){};
</script>
Answer: • typeof variableName;
Question:* Which of the following choices will change the source of the image to "image2.gif" when a user clicks on the image?
Answer: • img id="imageID" src="image1.gif" width="50" height="60" onmousedown="changeimg(image1.gif)" onmouseup="changeimg(image2.gif)"
Question:* How can created cookies be deleted using JavaScript?
Answer: • Overwrite with an expiry date in the past
Question:* What would be the value of 'ind' after execution of the following code?
var msg="Welcome to ExpertRating"
var ind= msg.substr(3, 3)
Answer: • com
Question:* Are the two statements below interchangeable?
object.property
object[''property'']
Answer: • Yes
Question:* Which of the following is not a valid method in generator-iterator objects in JavaScript?
Answer: • stop()
Question:* Which of the following code snippets will return all HTTP headers?
Answer: • var req = new XMLHttpRequest();
req.open('GET', document.location, false);
req.send(null);
var headers = req.getAllResponseHeaders().toLowerCase();
alert(headers);
Question:* Consider the following JavaScript alert:
<script type="text/JavaScript">
function message() {
alert("Welcome to ExpertRating!!!")
}
</script>
Which of the following will run the function when a user opens the page?
Answer: • body onload="message()"
Question:* Which of the following is the most secure and efficient way of declaring an array?
Answer: • var a = []
Question:* Which of the following Regular Expression pattern flags is not valid?
Answer: • p
Question:* Which of the following built-in functions is used to access form elements using their IDs?
Answer: • getElementById(id)
Question:* Which of the following statements is correct?
Answer: • Undefined object properties can be checked using the following code:
if (typeof something === "undefined")
alert("something is undefined");
Question:* Which of the following correctly uses a timer with a function named rearrange()?
Answer: • tmr=setTimeout("rearrange ()",1)
Question:* Which of the following can be used to escape the ' character?
Answer: • \
Question:* Which event can be used to validate the value in a field as soon as the user moves out of the field by pressing the tab key?
Answer: • onblur
Question:* When setting cookies with JavaScript, what will happen to the cookies.txt data if the file exceeds the maximum size?
Answer: • The file is truncated to the maximum length.
Question:* Which of the following are not global methods and properties in E4X?
Answer: • setName() and setNamespace()
Question:* Which of the following will change the color of a paragraph's text to blue when a user hovers over it, and reset it back to black when the user hovers out?
Answer: • <p onmouseover="style.color='blue'" onmouseout="style.color='black'"> The text of the paragraph..</p>
Question:* What is the purpose of while(1) in the following JSON response?
while(1);[['u',[['smsSentFlag','false'],['hideInvitations','false'],['remindOnRespondedEventsOnly','true'],['hideInvitations_remindOnRespondedEventsOnly','false_true'],['Calendar ID stripped for privacy','false'],['smsVerifiedFlag','true']]]]
Answer: • It makes it difficult for a third-party to insert the JSON response into an HTML document with a <script> tag.
Question:* Consider the three variables:
someText = 'JavaScript1.2';
pattern = /(\w+)(\d)\.(\d)/i;
outCome = pattern.exec(someText);
What does outCome[0] contain?
Answer: • JavaScript1.2
Question:* Which of the following choices will turn a string into a JavaScript function call (case with objects) of the following code snippet?
<script>
window.foo = {
bar: {
baz: function() {
alert('Hello!');
}
}
};
</script>
Answer: • window['foo']['bar']['baz']();
Question:* Which of the following determines whether cookies are enabled in a browser or not?
Answer: • (navigator.cookieEnabled)? true : false
Question:* Which of the following options can be used for adding direct support for XML to JavaScript?
Answer: • E4X
Question:* Which of the following will detect which DOM element has the focus?
Answer: • document.activeElement
Question:* Which of the following will randomly choose an element from an array named myStuff, given that the number of elements changes dynamically?
Answer: • randomElement = myStuff[Math.floor(Math.random() * myStuff.length)];
Question:* How can global variables be declared in JavaScript?
Answer: • Declare the variable between the 'script' tags, and outside a function to make the variable global
Question:* Which of the following objects in JavaScript contains the collection called "plugins"?
Answer: • Navigator
Question:* What will be output of the following code?
function testGenerator() {
yield "first";
document.write("step1");
yield "second";
document.write("step2");
yield "third";
document.write("step3");
}
var g = testGenerator();
document.write(g.next());
document.write(g.next());
Answer: • firststep1second
Question:* Which of the following methods will copy data to the Clipboard?
Answer: • execCommand('Copy')
Question:* Which of the following code snippets trims whitespace from the beginning and end of the given string str?
Answer: • str.replace(/^\s+|\s+$/g, '');
Question:* What is the difference between call() and apply()?
Answer: • The call() function accepts an argument list of a function, while the apply() function accepts a single array of arguments.
Question:* Which of the following code snippets is more efficient, and why?
<script language="JavaScript">
for(i=0;i<document.images.length;i++)
document.images[i].src="blank.gif";
</script>
<script language="JavaScript">
var theimages = document.images;
for(i=0;i<theimages.length;i++)
theimages[i].src="blank.gif"
</script>
Answer: • The second code is more efficient as it employs object caching.
Question:* What is the meaning of obfuscation in JavaScript?
Answer: • Making code unreadable using advanced algorithms.
Question:* Which of the following JavaScript Regular Expression modifiers finds one or more occurrences of a specific character in a string?
Answer: • +
Question:* Which of the following is not a valid JavaScript operator?
Answer: • ^
Question:* Which of the following code snippets returns "[object object]"?
Answer: • <script>
var o = new Object();
o.toString();
</script>
Question:* Which of the following can be used to invoke an iframe from a parent page?
Answer: • window.frames
Question:* Select the following function that shuffles an array?
Answer: • function shuffle(array) {
var tmp, current, top = array.length;
if(top) while(--top) {
current = Math.floor(Math.random() * (top + 1));
tmp = array[current];
array[current] = array[top];
array[top] = tmp;
}
return array;
}
Question:* Which of the following code snippets removes objects from an associative array?
Answer: • delete array["propertyName"];
Question:* What is the error in the statement: var charConvert = toCharCode('x');?
Answer: • toCharCode() is a non-existent method.
Question:* What value would JavaScript assign to an uninitialized variable?
Answer: • undefined
Question:* What does the following JavaScript code do?
contains(a, obj) {
for (var i = 0; i < a.length; i++) {
if (a[i] === obj) {
return true;
}
}
return false;
}
Answer: • It checks if an array contains 'obj'.
Question:* If an image is placed styled with z-index=-1 and a text paragraph is overlapped with it, which one will be displayed on top?
Answer: • The paragraph.
Question:* Which of the following code snippets gets an image's dimensions (height & width) correctly?
Answer: • var img = document.getElementById('imageid');
var width = img.clientWidth;
var height = img.clientHeight;
Question:* Which of the following are correct values of variableC, and why?
<script>
variableA = [6,8];
variableB =[7,9];
variableC = variableA + variableB;
</script>
Answer: • 6, 87 and 9. The + operator is not defined for arrays, and it concatenates strings, so it converts the arrays to strings.
Question:* The following are the samples for getting a selected value in the from a dropdown list:
<select id="ddlViewBy">
<option value="1">test1</option>
<option value="2" selected="selected">test2</option>
<option value="3">test3</option>
</select>
Which code block is correct?
Answer: • var e = document.getElementById("ddlViewBy");
var strUser = e.options[e.selectedIndex].value;
Question:* var profits=2489.8237
Which of the following code(s) produces the following output?
output : 2489.824
Answer: • profits.toFixed(3)
Question:* A form contains two fields named id1 and id2. How can you copy the value of the id2 field to id1?
Answer: • document.forms[0].id1.value=document.forms[0].id2.value
Question:* Which of the following code snippets will toggle a div element's background color?
<button id="toggle">Toggle</button>
<div id="terd">Change Background Color.</div>
Answer: • <script>
var button = document.getElementById('toggle');
button.onclick = function() {
terd.style.backgroundColor = terd.style.backgroundColor == 'blue' ? 'red' : 'blue';
};
</script>
Question:* How can the user's previously navigated page be determined using JavaScript?
Answer: • Using the window object
Question:* Which of the following is not a valid method for looping an array?
Answer: • var a= [1,2];
a.loop( function(item) {
alert(item);
})
Question:* Which of the following correctly sets a class for an element?
Answer: • document.getElementById(elementId).setAttribute("className", "Someclass");
Question:* An HTML form contains 10 checkboxes all named "chkItems". Which JavaScript function can be used for checking all the checkboxes together?
Answer: • function CheckAll() {
for (z = 0; z < document.forms[0].chkItems.length; z++) {
document.forms[0].chkItems[z].checked=true
}
}
Question:* Which of the following is a JavaScript comment?
Answer: • // comment
Question:* var foo = 'Global'; function fun() { log( foo ); var foo = 'Local'; log( foo ); } fun(); What the output of the above to log()?
Answer: • undefined Local
Question:* console.log( typeof [1,2] ) will print out:
Answer: • object
Question:* JavaScript is ...
Answer: • object based
Question:* Every object is linked to a _________ object from which it can inherit properties.
Answer: • prototype
Question:* What is the value of x? var x = typeof NaN;
Answer: • "number"
Question:* What will be the value of result? function foo(bar) { return bar ? bar == foo : foo(foo); } var result = foo();
Answer: • true
Question:* What values will the output function be called with, in the following code: var foo; var bar = { name: "baz", email: "fiz@example.com", sendmail: function() { } }; for (foo in bar) { output(foo); }
Answer: • "name", "email", "sendmail"
Question:* Consider: var x = ['a', 'b', 'c']; Which line of code will remove the first element of the array, resulting in x being equal to ['b', 'c']?
Answer: • x.splice(0, 1);
Question:* What is the value of x? var z = [typeof z, typeof y][0]; var x = typeof typeof z;
Answer: • "string"
Question:* var x = {}; var foo = function () { this.hello = "Hi"; return this; }; x.bar = foo; What is the value of the following code: x.bar().bar().hello;
Answer: • "Hi"
Question:* Which of the following assigned values of x will cause (x == x) to return false?
Answer: • All of the answers
Question:* What would this code print out? if (new Boolean(false)) console.log("True"); else console.log("False");
Answer: • True
Question:* Which two values are logged by the following code? var x = 5; (function () { console.log(x); var x = 10; console.log(x); }());
Answer: • undefined 10
Question:* Infinity * null will return :
Answer: • NaN
Question:* Assuming alert displays a string of its argument: var a = 10; function example(){ alert(a); var a = 5; } example(); What will be shown if the preceding code is executed?
Answer: • undefined
Question:* What is the result? "" ? "a" : "b"
Answer: • "b"
Question:* What is the value of x? var x = typeof null;
Answer: • "object"
Question:* The length property of an Array object is always:
Answer: • equal to the highest index of that object + 1
Question:* var data = [1, 2, 3, 4, 5, 6]; data.shift(); What does data look like?
Answer: • [2, 3, 4, 5, 6]
Question:* Which fact is true about the keyword "default"?
Answer: • It catches any case clauses not caught by case statements within a switch statement
Question:* Which String prototype method is capable of removing a character from a string?
Answer: • replace()
Question:* What is the value of x after the following statement? var x = 1 == '1';
Answer: • true
Question:* What is the result of the following code snippet? var small = 'BIG'; var BIG = 'small'; console.log(/small/.test(BIG)); console.log(/BIG/.test(small));
Answer: • true true
Question:* What is the result of the following statement: typeof "x";
Answer: • "string"
Question:* Is there a value type for individual string characters?
Answer: • No, there is only type "string" for characters.
Question:* Given a variable named stringVar with a string value, what does the following do? stringVar.toUpperCase();
Answer: • Return a copy of stringVar with all letters in uppercase
Question:* Which is an example of (only) an object literal in Javascript?
Answer: • var obj = { prop1: 'property 1', prop2: 'property 2' };
Question:* The loop isn't working. What's the problem? <code> var foos = ['a', 'b', 'c' , 'd', 'e']; var bars = ['x', 'y', 'z']; for (var i = 0; i < foos.length; i++) { var foo = foos[i]; for (var i = 0; i < bars.length; i++) { var bar = bars[i]; /* some code using `bar` */ } } </code>
Answer: •
The inner loop resets the outer for-loop, leaving it a fixed position
each time, causing an infinite loop (hint: no block scope).
Question:* Functions in javascript are always ..
Answer: • objects
Question:* How do you read the first character in a string?
Answer: • data.charAt(0);
Question:* Which of the following have special meanings within the language syntax?
Answer: • Reserved words
Question:* What is the result? 0 == ""
Answer: • true
Question:* Primitive types are passed by :
Answer: • Value
Question:* To what type are values converted internally when evaluating a conditional statement?
Answer: • boolean
Question:* var x = "foo"; x = !!x; What is the value of x?
Answer: • true
Question:* What will calling the below test function log to console? function test(){ console.log(a); var a = 'hello'; console.log(a); }
Answer: • undefined, "hello"
Question:* How do you assign an anonymous function to a variable?
Answer: • var anon = function() { };
Question:* What is the value of x? var x = 2 + "2";
Answer: • "22"
Question:* Which of these is not a JavaScript statement?
Answer: • None, these are all valid statements.
Question:* Which of the following variable types does not exist in JavaScript?
Answer: • double
Question:* Which of the following is a way to add a new value to the end of an array?
Answer: • arr[arr.length] = value;
Question:* What is the RegExp object constructor used for?
Answer: • Match text against regular expressions
Question:* What does "2" + 3 + 4 evaluate to?
Answer: • '234'
Question:* When an array index goes out of bounds, what is returned?
Answer: • undefined
Question:* Which is the correct syntax to write array literals in JavaScript?
Answer: • var x = ["blank","blank","blank"];
Question:* The "exploit" property:
Answer: • Does not exist in JavaScript
Question:* split() is a method of which constructors' prototype?
Answer: • String.prototype
Question:* Which of the following orders can be performed with the Array prototype "sort()" callback?
Answer: • All of these
Question:* var a = {1:'one',2:'two',3:'three'}; var b = Object.keys(a); What's the value of b?
Answer: • An array with all of the distinct keys from the obj a
Question:* How do you write a conditional statement that will *only* execute the contained code if variable x has a value 5 of type *number*?
Answer: • if (x === 5) { ... }
Question:* What is the value of c? var a = function(){ this.b = 1; } var b = function(){ var b = new a().b; return 5 + b; } var c = b();
Answer: • 6
Question:* How do you find the number with the highest value of x and y?
Answer: • Math.max(x, y)
Question:* What is the value of x? var a = false; var x = a ? “A” : “B”;
Answer: • "B"
Question:* Which of the following operators can assign a value to a variable?
Answer: • All of these
Question:* What is the value of x? var x = '1'+2+3;
Answer: • "123"
Question:* Which of the following is the equivalent of the following. if (a) { x = b; } else { x = c; }
Answer: • x = a ? b : c;
Question:* What is the value of x? var obj = {}; obj["function"] = 123; x = obj.function;
Answer: • 123
Question:* null === undefined
Answer: • false
Question:* Which event fires whenever a control loses focus?
Answer: • onblur
Question:* Which of these is not a logical operator?
Answer: • &
Question:* Which of these operators compares two variables by value AND type?
Answer: • ===
Question:* Which message does the following log to the console? bar(); function bar() { console.log('bar'); }
Answer: • "bar"
Question:* Which of the following invokes a user-defined object constructor function?
Answer: • var x = new myConstructor();
Question:* The function call Math.ceil(3.5) returns:
Answer: • 4
Question:* In JavaScript, to call a function directly, you use:
Answer: • function_expression ( arguments_if_any )
Question:* How do you declare a function?
Answer: • function doSomething() {}
Question:* How would one declare a string variable?
Answer: • Any of these
Question:* What is the value of a : var a = 3; var b = 2; var c = a; var a=b=c=1;
Answer: • 1
Question:* Properties of objects may be accessed using...
Answer: • the dot notation in JavaScript.
Question:* What is the value of the array myArr after execution of the following code: var myArr = [1,2,3,4,5]; myArr.shift();
Answer: • [2,3,4,5]
Question:* What does isNaN() do?
Answer: • Only returns true if the argument is not a number
Question:* What keyword is used to define the alternative path to take in a conditional statement?
Answer: • else
Question:* What is the difference between a while loop and a do...while loop?
Answer: • The code inside a do...while loop will always be executed at least once, even if the condition is false.
Question:* What is the difference between == and === ?
Answer: • The == operator converts both operands to the same type, whereas === returns false for different types.
Question:* Which of these could be a correct way to create an instance of Person?
Answer: • var john = new Person('John', 'Doe', 50, 'blue');
Question:* (function( ) { var x = foo( ); function foo( ){ return "foobar" }; return x; })( ); What does this function return?
Answer: • "foobar"
Question:* What operator is used for string concatenation?
Answer: • +
Question:* Which is the correct way to write a JavaScript array?
Answer: • var names = ["Tim","Kim","Jim"];
Question:* USERNAME and userName
Answer: • Represent the name of different variables
Question:* Which of these descriptors applies to JavaScript?
Answer: • Loosely typed, values of any type can be assigned to any variable.
Question:* Which of the following is an Error object constructor?
Answer: • All of these
Question:* How do you check what the type of a value in variable x is?
Answer: • typeof(x);
Question:* Which of the following is a JavaScript comment?
Answer: • // comment
Question:* What is the value of the following expression: 8 % 3
Answer: • 2
Question:* var a = '011'; parseInt(a); will return:
Answer: • 11
Question:* var a = '011'; parseInt(a); will return:
Answer: • 11
Question:* How does a "while" loop start?
Answer: • while (i<=10)
Question:* The `else` statement is ___
Answer: • used together with the `if` statement to specify the code that should execute when the `if` condition is false.
Question:* Given the following code, what does myFunc() return? var foo = 'foo'; var bar = 'bar'; function myFunc() { return foo + bar; }
Answer: • "foobar"
Question:* String literals are written using:
Answer: • Either double quotes or single quotes: "example" and 'example'
Question:* How is an object property referenced?
Answer: • myObj.foo
Question:* Which symbol is not used in logical operations?
Answer: • %
Question:* Which of these will throw a SyntaxError?
Answer: • if (x ==== 1) { }
Question:* JavaScript supports dynamic typing, you can assign different types of values to the same variable.
Answer: • true
Question:* How do you round the number 7.25, to the nearest whole number?
Answer: • Math.round(7.25)
Question:* How to return the first value of this array? var myArr = [1, 2, 3, 4, 5]; var myVal = ...
Answer: • myArr[0];
Question:* How do you define a function called "fName"?
Answer: • function fName() { }
Question:* Which of the following is not a reserved word?
Answer: • program
Question:* Which of the following asserts that the variables `A`, `B`, and `C` have unequal values?
Answer: • A !== B && B !== C && A !== C
Question:* What does the "break" statement do?
Answer: • Aborts the current loop or switch statement.
Question:* Which of the following is a valid function definition?
Answer: • function myFunc(arg1,arg2) { }
Question:* Which of the following declares a variable with a value of string type?
Answer: • var myVar = "This is a string";
Question:* Are variable identifiers case-sensitive?
Answer: • Yes
Question:* What is the correct JavaScript syntax to insert a comment that can span multiple lines?
Answer: • /* This comment has more than one line */
Question:* The "if" statement is used to:
Answer: • Deal with logic that should execute only when a condition is true
Question:* Which keyboard character represents the assignment operator?
Answer: • =
Question:* String concatenation...
Answer: • Is the combination of two or more text Strings
Question:* Properties of a RegExp object include:
Answer: • All of these
Question:* You use the Math.pow() method to:
Answer: • Return a number raised to the power of a second number
Question:* What is the value of ("dog".length)?
Answer: • 3
Question:* Which is NOT a way to create a loop in javascript?
Answer: • repeat (...) { }
Question:* What is the value of x? var a = "A"; var x = a.concat("B");
Answer: • "AB"
Question:* Which statement loops through an array?
Answer: • for (var i=0; i < myArray.length; i++)
Question:* The var statement is used to:
Answer: • Create a new local variable
Question:* function foo(){ var tmp = 'one_two_three_four_five'; return tmp.replace(/_/g, '+'); } What does foo() return?
Answer: • one+two+three+four+five
Question:* A for loop is written as such: "for (first property; second property; third property) {...}" What does the third property represent?
Answer: • An action to take at the end of the current loop cycle
Question:* Where do you use the "break" statement?
Answer: • To terminate a switch statement, loop, or labeled block.
Question:* In an array object, what is the key of the first value?
Answer: • 0
Question:* Which of the following primitive values exist in JavaScript?
Answer: • All of these
Question:* What keyword is used to begin a conditional statement?
Answer: • if
Question:* What character ends a javascript statement?
Answer: • A semicolon ";".
Question:* Which has the correct syntax of a ternary operation?
Answer: • var x = y === true ? "true" : "false";
Question:* JavaScript is an implementation of the ______ language standard.
Answer: • ECMAScript
Question:* If a function doesn't explicitly use the "return" operator, what will the return value be when the function is invoked?
Answer: • undefined
Question:* What is result of the following expression: var a = "test"; console.log(!!a);
Answer: • true
Question:* What is the name of the String prototype that appends the given string to the base string and returns the new string?
Answer: • "x".concat("foo")
Question:* Which of these is a correct method to create a new array?
Answer: • var myArray = [];
Question:* var data = ["A", "B", "C", "D"]; data.unshift("X"); data.push("Y"); What does data look like?
Answer: • ["X", "A", "B", "C", "D", "Y"]
Question:* What character combination is used to create a single line comment?
Answer: • //
Question:* Which of the following is the syntax for an object literal (with no properties)?
Answer: • {};
Question:* How can you concatenate multiple strings?
Answer: • Both of these
Question:* How do you assign object properties?
Answer: • obj["age"] = 25 OR obj.age = 25
Question:* Consider this code: var x = ['Hello']; What value will 'x[1]' return?
Answer: • undefined
Question:* The _______ operator returns a string that identifies the type of its operand.
Answer: • typeof
Question:* When writing an object literal, what is used to separate the properties from each other?
Answer: • a comma ","
Question:* What are curly braces ("{" and "}") used for?
Answer: • Block declarations and object literals
Question:* What is the value of x? function foo(y) { var z = 10; z = 7; }; var x = foo("bar");
Answer: • undefined
Question:* How do you create an object in JavaScript?
Answer: • All of these work.
Question:* Which of the following is not a method in the "JSON" object according to the ECMAScript specification?
Answer: • JSON.fromString
Question:* How can you get the number of characters in a string ?
Answer: • "1234567".length
Question:* What is the result of the following statement: 0 == "";
Answer: • true
Question:* What does null, undefined, "string", 20, true and false have in common?
Answer: • they are primitive values
Question:* Given the following code, what is the value of x? var x = ['foo', 'bar']; x.length = 1;
Answer: • ["foo"]
Question:* Math.random() returns..
Answer: • a random number between 0 and 1
Question:* What is the result of the following expression? ({"foo": true}).foo;
Answer: • true
Question:* In the loop, "for (first clause; second clause; third clause) { statements; }" What does the second clause represent?
Answer: • A condition to check at the beginning of each loop cycle
Question:* What is the value of `x` after the following? var x = "hello"; (function() { x = "goodbye"; }());
Answer: • "goodbye"
Question:* Which is not a primitive data type in JavaScript?
Answer: • character
Question:* What will invoking `foo` return? function foo() { var x = 10; x = 7; };
Answer: • undefined
Question:* What is the value of x? var str = "what is this"; var x = str.search("is");
Answer: • 5
Question:* The "this" keyword refers to ...
Answer: • current execution context (could be any value).
Question:* '&' Operator is _____
Answer: • a bitwise operator
Question:* What character combination is used to alter the order of operations by grouping expressions?
Answer: • ( )
Question:* var x = Math.ceil(10.126); What is the value of x?
Answer: • 11
Question:* What is the type of `null`, according to the `typeof` operator?
Answer: • "object"
Question:* function b(x, y, a) { arguments[2] = 10; alert(a); } b(1, 2, 3); What is alerted?
Answer: • 10
Question:* What is the difference between using call() and apply() to invoke a function with multiple arguments?
Answer: • apply() is identical to call(), except apply() requires an array as the second parameter
Question:* var y = 3, x = y++; What is the value of x?
Answer: • 3
Question:* Which of the following types does NOT exist in javascript?
Answer: • integer
Question:* What is the end value of myAddedVar with the following code: var myVar = '5'; var myAddedVar = myVar + 10;
Answer: • '510'
Question:* What does this line do? variable++;
Answer: • Increments the value of "variable" but returns the previous value
Question:* var a = new Boolean(false); What is (typeof a)?
Answer: • 'object'
Question:* What is the value of x? var x = typeof new String("abc");
Answer: • object
Question:* Which of these will invoke a function?
Answer: • function.apply(...)
Question:* Does NaN equal itself?
Answer: • No, NaN does not equal itself (== comparison would return false).
Question:* What will happen in the console after executing this code? if ("foo") { console.log("foo" === false); console.log("foo" === true); }
Answer: • false false
Question:* What is the value of the function log? var _ = '_'; log(parseInt(_));
Answer: • NaN
Question:* Which of these is not a built-in object constructor?
Answer: • Time
Question:* Given the following code: var myVar = '5'; var myAddedVar = myVar + 10; What is the value of (myAddedVar.constructor === Number)?
Answer: • false
Question:* How would you iterate over the following object? var my_data = {a: 'Ape', b: 'Banana', c: 'Citronella'};
Answer: • for (var key in my_data) {}
Question:* What is the value of x after the following code is executed? var x = 0; x = x++;
Answer: • 0
Question:* You use the Math.tan( ) method to:
Answer: • Return the tangent of an angle (in radians)
Question:* A javascript variable prefixed with a $ is:
Answer: • valid javascript syntax as any other character
Question:* Math.min() < Math.max(); ...will return:
Answer: • false
Question:* Math.min() < Math.max(); will return
Answer: • false
Question:* What does the following expression return? 1 + 5 + " bottles of milk";
Answer: • "6 bottles of milk"
Question:* Which Object method takes a `propertyName` parameter and returns `true` if the object contains an uninherited property with that key?
Answer: • obj.hasOwnProperty('propertyName');
Question:* var foo = "Global"; function fun() { log( foo ); var foo = "Local"; log( foo ); } fun(); What the output of the above to log()?
Answer: • undefined Local
Question:* Which of the following is NOT a valid way to write a loop that will iterate over the values in the array in variable "myArray"?
Answer: • None of these, they are all valid
Question:* What is the value of c? var A = function () { this.b = 1; } A.prototype.b = 2; var c = new A().b;
Answer: • 1
Question:* What will be the value of x? function A() { this.do = function () { return 'foo'; }; } A.prototype = { do: function () { return 'bar'; } }; var x = new A().do();
Answer: • "foo"
Question:* What is the right way to combine two arrays into a new array? var a = ["a", "b", "c"]; var b = ["d", "e", "f"];
Answer: • var c = a.concat(b);
Question:* What is the output? var one; var two = null; console.log(one == two, one === two);
Answer: • true false
Question:* Which are the different ways to affect the "this" reference in a function?
Answer: • Invoking a function with the "new" keyword, invoking through the .call() method, invoking through the .apply() method.
Question:* What is the difference between the two declaration methods below? var functionOne = function() { /* some code */ } function functionTwo() { /* some code */ }
Answer: •
functionOne is defined in-place (until that line, functionOne is
undefined), whereas functionTwo is hoisted to the top of the scope and
is available as a function throughout the scope.
Question:* How does JavaScript interpret numeric constants outside of strict mode?
Answer: • As octal if they are preceded by a zero, and as hexadecimal if they are preceded by a zero and "x"
Question:* When reserved words are used as keys in object literals they must be ______?
Answer: • quoted
Question:* Mathematical expression, "10" - (12+5).toString(), evaluates to what?
Answer: • -7
Question:* What does the following return? Number(null);
Answer: • 0
Question:* What is the value of x.length after running this code? x = ["foo"]; x.quux = "Hello"; x[1] = "bar";
Answer: • 2
Question:* What is the value of x after the code below is executed? var x = ""; function foo() { x += "foo "; } var bar = function() { x += "bar "; }; foo(); var quux = bar = foo; quux();
Answer: • "foo foo "
Question:* What will be in console after executing this code: console.log(1 + '1' - 1);
Answer: • 10
Question:* The expression (typeof NaN === "number") evaluates to:
Answer: • true
Question:* What will: typeof typeof(null) return?
Answer: • string
Question:* What will the expression a === b return after the following? var a = { "foo": "bar" }; var b = { "foo": "bar" };
Answer: • false
Question:* How can you remove an element from an array and replace it with a new one ?
Answer: • array.splice(...)
Question:* What will we see in the console after the following code run: var a = 'Bolt'; function f() { if (!a) { var a = 'Nut'; } console.log(a); } f(); console.log(a);
Answer: • 'Nut' then 'Bolt'
Question:* true + true will return :
Answer: • 2
Question:* What is the result of: function foo() { output( "biz " + bar() ); } bar(); var bar = function() { return "baz"; }
Answer: • TypeError: Undefined is not a function
Question:* What is the value of x? var x = 10/0;
Answer: • Infinity
Question:* What will be the result of this expression: void 0
Answer: • undefined
Question:* What does Math.random() do?
Answer: • Returns a random number from and including 0 to less than 1.
Question:* In the following code: function test() { var foo = bar = 5; } test();
Answer: • Variable foo is a local variable. But bar is a global variable.
Question:* What are the values of x and y after the invocation of `foo` in following? var x = "I am global x"; var y = "I am global y"; function foo() { var y = x = "Hello from foo"; } foo();
Answer: • x = "Hello from foo"; y = "I am global y";
Question:* var q = null; q++; What is q?
Answer: • 1
Question:* Given the following code, what will myFunction(123, false, "test") return? function myFunction(param) { return arguments[1] || param; }
Answer: • 123
Question:* After the following code: var a = function(){ this.b = 1; this.deleteMe = function(){ delete this; } }; var c = new a(); c.deleteMe(); What is the value of (String(c))?
Answer: • [object Object]
Question:* Which operator has highest precedence?
Answer: • *
Question:* function Question() { this.answered = false; } Question.prototype.rightAnswer = 5; console.log( new Question().rightAnswer, Question.rightAnswer ); What gets printed to the console?
Answer: • 5 undefined
Question:* What will the console log when running this code? Function.prototype.a = 1; var a = new Function(); a.prototype.a = 2; var c = new a(); console.log(a.a , c.a);
Answer: • 1 2
Question:* Evaluate: undefined + 2
Answer: • NaN
Question:* Evaluate: new Boolean(new Boolean(false)).valueOf()
Answer: • true
Question:* An (inner) function enjoys access to the parameters and variables of all the functions it is nested in. This is called:
Answer: • Lexical scoping
Question:* Object.keys(x)
Answer: • returns the enumerable properties of x as an array of strings.
Question:* "bar".split().length returns:
Answer: • 1
Question:* Math.Pi returns the mathematical constant of Pi. What standard JavaScript method would truncate Math.Pi to 3.14 ?
Answer: • Math.Pi.toFixed(2)
Question:* function foo(){ var tmp = 'one_two_three_four_five'; return tmp.replace('_', '+'); } What does foo() return?
Answer: • one+two_three_four_five
Question:* var x = { foo: "A" }; x.constructor.prototype.foo = "B"; var y = {}; console.log(x.foo); console.log(y.foo); Which two values will be logged?
Answer: • "A" "B"
Question:* Evaluate the following expression: ~-(2 + "2")
Answer: • 21
Question:* Which of these will create a copy of an array such that changes to the old array will not be reflected in the new array?
Answer: • var newArray = oldArray.slice(0);
Question:* What is the output of the following? var x = 1; console.log(x++ + ++x + x);
Answer: • 7
Question:* console.log( ~[]+~![]+~!![] ); Console output is:
Answer: • -4
Question:* What value is passed to function "foo" as first argument? foo( +"5" );
Answer: • 5
Question:* What will be printed to the console as a result of this code? var printName = function() { console.log('Matt'); printName = function() { console.log('James'); }; }; var copy = printName; printName(); copy();
Answer: • Matt Matt
Question:* What is the result of: console.log((!+[]+[]+![]).length);
Answer: • 9
Question:* What is the value of x after the following code is run? var obj = { 0: 'who', 1: 'what', 2: 'idontknow'}; var x = 1 in obj;
Answer: • true
Question:* Which of the following String prototype method takes a regular expression?
Answer: • search()
Question:* What is the value of mike after this code is run? function Person(name, age) { this.name = name; this.age = parseInt(age, 10); } var mike = Person('Mike', '25');
Answer: • undefined
Question:* var x = ([]+!![])[+!+[]]; What is the value of x?
Answer: • 'r'
Question:* Which of the following expressions evaluates to false?
Answer: • new Boolean('false') == false
Question:* Math.log(x) returns:
Answer: • Logarithm base e (Euler's number) of x.
Question:* Which of the following is not a reserved word in the language?
Answer: • and
Question:* What is the result of the below expression? Assume output is a function that outputs a line of text. output(typeof (function() {output("Hello World!")})());
Answer: • Hello World! undefined
Question:* What is the value of "x" after the following code runs? var x; x++;
Answer: • NaN
Question:* function foo() { this = "foo"; } var a = foo(); What will the preceding code produce?
Answer: • ReferenceError: Invalid left-hand side in assignment
Question:* What will this code produce: +new Date()
Answer: • Unix timestamp in milliseconds (UTC timezone)
Question:* What is the value of c? var a = function(){ this.b = 1; } var b = function(){ this.b = new a().b; return 5; } var c = b() + new b();
Answer: • Error thrown when running the code
Question:* Which of the following Array prototype method actually modifies the array it's been called on?
Answer: • splice()
Question:* What does the following return? Math.max();
Answer: • -Infinity
Question:* Which are the different value types in JavaScript?
Answer: • boolean, number, string, function, object and undefined
Question:* String values have a "length" property. Why is this property not included in a for-in loop over a string object? var prop, str; str = 'example'; /* str.length === 7 */ for ( prop in str) {}
Answer: • Because the "length" property has internal [[Enumerable]] set to false.
Question:* What will the following code, when evaluated, do? var void = function () {};
Answer: • Throw a SyntaxError
Question:* Object("s") instanceof String === "s" instanceof String
Answer: • false
Question:* What's the correct syntax for creating a Date object for January 10, 1998?
Answer: • new Date(1998, 0, 10);
Question:* Evaluate: ![]+[]
Answer: • 'false'
Question:* What is the value of x? var a = "abc"; var x = a instanceof String;
Answer: • false
Question:* Which of the following is NOT a reserved word in JavaScript?
Answer: • array
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