Javascript - Quiz - Jan 2016

When a variable that is not declared is used it returns “undefined”

When a variable that is not declared is used it throws ReferenceError

A function that is defined below in the later part of the script can be invoked / referred

A variable that is not assigned any value returns “undefined”

Int, float, double, char, Boolean

Int, float, double, char, String, Boolean

Number, String, Boolean

Number, char, String, Boolean

var myObject = new Object(proto);

var myObject = new Object();
myObject.prototype = proto;

var myObject = Object.create(proto);

var myObject[“prototype”] = proto;

Only var myArray = new Array();

Only var myArray = [];

var myArray[] = new Object();

Both a & b

function SubClass() { super(); }

function SubClass() { ParentClass(); }

function SubClass() { new ParentClass(); }

function SubClass() { ParentClass.apply(this, arguments); }

All of the above

var mySingleton = function() {
function SingletonClass() {
}
return new SingletonClass();
};

b. var mySingleton = (function() {
function SingletonClass() {
}
return new SingletonClass();
})();

var mySingleton = {};

It is not possible to create a singleton object using function

A special scope variable assigned to function that holds states / variables that was accessible at the time of defining this inner function

Closure is a property of function that needs to be explicitly assigned within the body of function

Closure is a global function along with global variables

Closure is an inner function along with global variables

function invokeCallback(callback) {
for(var i=0;i<5;i++) {
setTimeout(callback(i), 500);
}
}

function invokeCallback(callback) {
for(var i=0;i<5;i++) {
setTimeout(function() {callback(i)}, 500);
}
}

function invokeCallback(callback) {
function invoker(i) {
return function() { callback(i); }
}
for(var i=0;i<5;i++) {
setTimeout(invoker(), 500);
}
}

None of the above

Array.removeDuplicates = removeDuplicates;

Array.prototype.removeDuplicates = removeDuplicates

var myArray = new Array() {
this.removeDuplicates = removeDuplicates;
}

Array is a predefined type in javascript. It cannot be modified.

Through constructor inheritance

Using extends keyword

Through prototype chaining

There is no automatic support in Javascript. Properties and behaviors need to be explicitly added

“!==” will not check for null or undefined or “” while “!=” checks

“!=” does not convert type while “!==” does convert type

“!==” does not do type coercion while “!= does type coercion

Both operators are same

xhr.send(JSON.stringify(myJsonObject));

xhr.open(‘post’, myUrl, JSON.stringify(myJsonObject));

xhr.open(JSON.stringify(myJsonObject));

xhr.open(‘post’, myUrl + “?” +
JSON.stringify(myJsonObject));

var childDiv = window.createElement(“div”);
window.getElementById(“parentDiv”).appendChild(childDiv);

var childDiv = document.newElement(“div”);
document.getElementById(“parentDiv”).appendChild(childDiv);

var childDiv = document.createElement(“<div
id=”childDiv”);
window.getElementById(“parentDiv”).appendChild(childDiv);

var childDiv = document.createElement(“div”);
childDiv.setAttribute(“id”, “childDiv”);
document.getElementById(“parentDiv”).appendChild(childDiv);

Keep Javascript files separate and download them individually

Concatenate multiple javascript files into single javascript file and refer to this javascript in the script tag

Use descriptive variable names and detailed comments

Minify javascript to reduce the overall size of Javascript file downloaded by browser

Use CDN site over local Javascript files