4388315
Descrição
Quiz por arunram.krish, atualizado more than 1 year ago
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Criado por arunram.krish
quase 9 anos atrás
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Questão 1
Questão
What are the values that evaluate to false when used in a Boolean expression?
Responda
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Only null
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Only undefined
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Only “”
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Only NaN
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All of the above
Questão 2
Questão
Which of the following statements are TRUE?
Responda
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When a variable that is not declared is used it returns “undefined”
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When a variable that is not declared is used it throws ReferenceError
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A function that is defined below in the later part of the script can be invoked / referred
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A variable that is not assigned any value returns “undefined”
Questão 3
Questão
What are the primitive types in Javascript?
Responda
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Int, float, double, char, Boolean
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Int, float, double, char, String, Boolean
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Number, String, Boolean
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Number, char, String, Boolean
Questão 4
Questão
How do you create an Object with a prototype object assigned to variable “proto”?
Responda
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var myObject = new Object(proto);
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var myObject = new Object(); myObject.prototype = proto;
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var myObject = Object.create(proto);
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var myObject[“prototype”] = proto;
Questão 5
Questão
How to create a Javascript array?
Responda
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Only var myArray = new Array();
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Only var myArray = [];
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var myArray[] = new Object();
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Both a & b
Questão 6
Questão
How do you invoke parent class’ constructor (by name ParentClass) from a sub class constructor (by name SubClass) to inherit properties defined in ParentClass in the new SubClass object?
Responda
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function SubClass() { super(); }
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function SubClass() { ParentClass(); }
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function SubClass() { new ParentClass(); }
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function SubClass() { ParentClass.apply(this, arguments); }
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All of the above
Questão 7
Questão
How do you use function to create a singleton object?
Responda
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var mySingleton = function() { function SingletonClass() { } return new SingletonClass(); };
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b. var mySingleton = (function() { function SingletonClass() { } return new SingletonClass(); })();
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var mySingleton = {};
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It is not possible to create a singleton object using function
Questão 8
Questão
What is a Closure?
Responda
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A special scope variable assigned to function that holds states / variables that was accessible at the time of defining this inner function
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Closure is a property of function that needs to be explicitly assigned within the body of function
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Closure is a global function along with global variables
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Closure is an inner function along with global variables
Questão 9
Questão
How do you invoke a callback function within a loop with loop index variable as argument after 500 milliseconds?
Responda
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function invokeCallback(callback) { for(var i=0;i<5;i++) { setTimeout(callback(i), 500); } }
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function invokeCallback(callback) { for(var i=0;i<5;i++) { setTimeout(function() {callback(i)}, 500); } }
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function invokeCallback(callback) { function invoker(i) { return function() { callback(i); } } for(var i=0;i<5;i++) { setTimeout(invoker(), 500); } }
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None of the above
Questão 10
Questão
How do you add a function “removeDuplicates” (already defined with this name) accessible from all Array objects?
Responda
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Array.removeDuplicates = removeDuplicates;
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Array.prototype.removeDuplicates = removeDuplicates
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var myArray = new Array() { this.removeDuplicates = removeDuplicates; }
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Array is a predefined type in javascript. It cannot be modified.
Questão 11
Questão
How does Javascript object inherit properties and methods defined in ancestor classes?
Responda
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Through constructor inheritance
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Using extends keyword
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Through prototype chaining
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There is no automatic support in Javascript. Properties and behaviors need to be explicitly added
Questão 12
Questão
What is the difference between “!=” and “!==”?
Responda
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“!==” will not check for null or undefined or “” while “!=” checks
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“!=” does not convert type while “!==” does convert type
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“!==” does not do type coercion while “!= does type coercion
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Both operators are same
Questão 13
Questão
How do you pass JSON data as part of HTTP POST request body in AJAX request?
Responda
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xhr.send(JSON.stringify(myJsonObject));
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xhr.open(‘post’, myUrl, JSON.stringify(myJsonObject));
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xhr.open(JSON.stringify(myJsonObject));
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xhr.open(‘post’, myUrl + “?” + JSON.stringify(myJsonObject));
Questão 14
Questão
How do you create a “div” element with id “childDiv” and append it to parent div with id “parentDiv” using DOM API?
Responda
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var childDiv = window.createElement(“div”); window.getElementById(“parentDiv”).appendChild(childDiv);
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var childDiv = document.newElement(“div”); document.getElementById(“parentDiv”).appendChild(childDiv);
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var childDiv = document.createElement(“<div id=”childDiv”); window.getElementById(“parentDiv”).appendChild(childDiv);
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var childDiv = document.createElement(“div”); childDiv.setAttribute(“id”, “childDiv”); document.getElementById(“parentDiv”).appendChild(childDiv);
Questão 15
Questão
Choose the best practices that need to be adopted in production environment to improve the performance?
Responda
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Keep Javascript files separate and download them individually
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Concatenate multiple javascript files into single javascript file and refer to this javascript in the script tag
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Use descriptive variable names and detailed comments
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Minify javascript to reduce the overall size of Javascript file downloaded by browser
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Use CDN site over local Javascript files
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