UpWork (oDesk) & Elance JavaScript Test Question & Answers

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Ques : Which of the following prints "AbBc"?

Ans  : var b = 'a'; var result = b.toUpperCase() + 'b' + 'b'.toUpperCase() +'C'['toLowerCase'](); alert(result);

Ques : Performance-wise, which is the fastest way of repeating a string in JavaScript?
Ans  : 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; };

Ques : 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;
Ans  : 10

Ques : Which of the following code snippets changes an image on the page?
Ans  : var img = document.getElementById("imageId"); img.src = "newImage.gif";

Ques : Which of the following results is returned by the JavaScript operator "typeof" for the keyword "null"?
Ans  : object

Ques : Which of the following will check whether the variable vRast exists or not?
Ans  :  if (typeof vRast =="undefined") {}

Ques : Which of the following choices will change the source of the image to "image2.gif" when a user clicks on the image?
Ans  : img id="imageID" src="image1.gif" width="50" height="60" onmousedown="changeimg(image1.gif)" onmouseup="changeimg(image2.gif)"

Ques :  Which of the following Regular Expression pattern flags is not valid?
Ans  : p

Ques : Which of the following statements is correct?
Ans  : Undefined object properties can be checked using the following code: if (typeof something === "undefined") alert("something is undefined");

Ques : Which of the following choices will turn a string into a JavaScript function call (case with objects) of the following code snippet?

Ans  : window['foo']['bar']['baz']();

Ques : Which of the following options can be used for adding direct support for XML to JavaScript?
Ans  : E4X

Ques : Which of the following will detect which DOM element has the focus?
Ans  : document.activeElement

Ques : Which of the following will randomly choose an element from an array named myStuff, given that the number of elements changes dynamically?
Ans  :  randomElement = myStuff[Math.floor(Math.random() * myStuff.length)];

Ques : Which of the following objects in JavaScript contains the collection called "plugins"?
Ans  : Navigator

Ques : What is the difference between call() and apply()?
Ans  : The call() function accepts an argument list of a function, while the apply() function accepts a single array of arguments.

Ques : Select the following function that shuffles an array?
Ans  :  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; }

Ques : Which of the following code snippets removes objects from an associative array?
Ans  : delete array["propertyName"];

Ques : What is the error in the statement: var charConvert = toCharCode('x');?
Ans  :  toCharCode() is a non-existent method.

Ques : 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;
}
Ans  :  It checks if an array contains 'obj'.

Ques : 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?
Ans  : The paragraph.

Ques : Which of the following code snippets gets an image's dimensions (height & width) correctly?
Ans  : var img = document.getElementById('imageid'); var width = img.clientWidth; var height = img.clientHeight;

Ques : var profits=2489.8237

Which of the following code(s) produces the following output?

output : 2489.824
Ans  : profits.toFixed(3)

Ques : A form contains two fields named id1 and id2.  How can you copy the value of the id2 field to id1?
Ans  : document.forms[0].id1.value=document.forms[0].id2.value

Ques : Which of the following is true about setTimeOut()?
Ans  : The statement(s) it executes run(s) only once.

Ques : How can the operating system of the client machine be detected?
Ans  :  Using the navigator object

Ques : 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;
Ans  : 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.

Ques : Consider the following variable declarations:

var a="adam"
var b="eve"

Which of the following would return the sentence "adam and eve"?
Ans  : a.concat(" and ", b)

Ques : Which object can be used to ascertain the protocol of the current URL?
Ans  : location

Ques : Which of the following best describes a "for" loop?
Ans  : "for" loop consists of three optional expressions, enclosed in parentheses and separated by semicolons, followed by a statement executed in the loop.

Ques : Which of the following is not a valid HTML event?
Ans  :  onblink

Ques : Which of the following are JavaScript unit testing tools?
Ans  : Buster.js, YUI Yeti, Jasmine

Ques : Which of the following can be used for disabling the right click event in Internet Explorer?
Ans  :  event.button == 2

Ques : 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?
Ans  : reduceRight()

Ques : What will be the final value of the variable "apt"?

var apt=2;
apt=apt<<2 b="">
Ans  : 8

Ques :  How can a JavaScript object be printed?
Ans  : console.log(obj)

Ques : Which of the following is the correct syntax for using the JavaScript exec() object method?
Ans  : RegExpObject.exec(string)

Ques : Having an array object var arr = new Array(), what is the best way to add a new item to the end of an array?
Ans  : arr.push("New Item")

Ques : 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?
Ans  :  input name=txtId type="text" onblur="return ValidateField()"

Ques : Which of following uses the "with" statement in JavaScript correctly?
Ans  : with (document.getElementById("blah").style) { background = "black"; color = "blue"; border = "1px solid green"; }

Ques : Which of the following modifiers must be set if the JavaScript lastIndex object property was used during pattern matching?
Ans  : g

Ques : 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
        temp='''' + field.value.substring(i,i+1)

        if(valid.indexOf(temp)==''-1'') {
                ok=''no'';
        }
    }

    if(ok==''no'') {
        alert(''error'');
        field.focus();
    }
}
Ans  : It will force a user to enter only English alphabet character values.

Ques : How can created cookies be deleted using JavaScript?
Ans  : Overwrite with an expiry date in the past

Ques : What would be the value of 'ind' after execution of the following code?

var msg="Welcome to ExpertRating"
var ind= msg.substr(3, 3)
Ans  : com

Ques : Are the two statements below interchangeable?

object.property
object[''property'']
Ans  :  Yes

Ques :  Which of the following is not a valid method in generator-iterator objects in JavaScript?
Ans  : stop()

Ques : Which of the following code snippets will return all HTTP headers?
Ans  : var req = new XMLHttpRequest(); req.open('GET', document.location, false); req.send(null); var headers = req.getAllResponseHeaders().toLowerCase(); alert(headers);

Ques :  Which of the following is the most secure and efficient way of declaring an array?
Ans  :  var a = []

Ques : Which of the following built-in functions is used to access form elements using their IDs?
Ans  :  getElementById(id)

Ques : Which of the following correctly uses a timer with a function named rearrange()?
Ans  : tmr=setTimeout("rearrange ()",1)

Ques : Which of the following can be used to escape the ' character?
Ans  :  \

Ques : 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?
Ans  : onblur

Ques : When setting cookies with JavaScript, what will happen to the cookies.txt data if the file exceeds the maximum size?
Ans  : The file is truncated to the maximum length.

Ques : Which of the following are not global methods and properties in E4X?
Ans  :  setName() and setNamespace()

Ques : 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']]]]
Ans  : It makes it difficult for a third-party to insert the JSON response into an HTML document with a script tag.
Ques : Consider the three variables:

someText = 'JavaScript1.2';
pattern = /(\w+)(\d)\.(\d)/i;
outCome = pattern.exec(someText);

What does outCome[0] contain?
Ans  :  JavaScript1.2

Ques : Which of the following determines whether cookies are enabled in a browser or not?
Ans  : (navigator.cookieEnabled)? true : false

Ques : How can global variables be declared in JavaScript?
Ans  :  Declare the variable between the 'script' tags, and outside a function to make the variable global

Ques : 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());
Ans  : firststep1second

Ques : Which of the following methods will copy data to the Clipboard?
Ans  : execCommand('Copy')

Ques : Which of the following code snippets trims whitespace from the beginning and end of the given string str?
Ans  : str.replace(/^\s+|\s+$/g, '');

Ques : What is the meaning of obfuscation in JavaScript?
Ans  : Making code unreadable using advanced algorithms.

Ques : Which of the following JavaScript Regular Expression modifiers finds one or more occurrences of a specific character in a string?
Ans  : +

Ques : Which of the following is not a valid JavaScript operator?
Ans  :  ^    

Ques : Which of the following can be used to invoke an iframe from a parent page?
Ans  :  window.frames

Ques : What value would JavaScript assign to an uninitialized variable?
Ans  : undefined

Ques : How can the user's previously navigated page be determined using JavaScript?
Ans  :  Using the window object

Ques : Which of the following is not a valid method for looping an array?
Ans  :  var a= [1,2]; a.loop( function(item) { alert(item); })

Ques : Which of the following correctly sets a class for an element?
Ans  :  document.getElementById(elementId).setAttribute("className", "Someclass");

Ques : An HTML form contains 10 checkboxes all named "chkItems". Which JavaScript function can be used for checking all the checkboxes together?
Ans  : function CheckAll() { for (z = 0; z < document.forms[0].chkItems.length; z++) { document.forms[0].chkItems[z].checked=true } }

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