Front End Developers-Lab

(JS) JavaScript
Top 6 Interview Questions and Anwsers

1- What is this , bind?




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The bind() method creates a new function that, when called, has its this keyword set to the provided value, with a given sequence of arguments preceding any provided when the new function is called.

Example


//JavaScript Demo: Function.bind()
var module = {
  x: 42,
  getX: function() {
    return this.x;
  }
}


var unboundGetX = module.getX;
console.log(unboundGetX()); 
//The function gets 
invoked at the global scope 
// expected output: undefined 

var boundGetX = 
unboundGetX.bind(module);
console.log(boundGetX());
// expected output: 42

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2- What Are Javascript Data Types?




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JavaScript supports three Primary, two Composite and two Special data types.
Next, we list down the data types in each of the categories.

Primary Data Types.
String
Number
Boolean

Composite Data Types.
Object
Array

Special Data Types.
Null
Undefined



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3- What Are The Different Ways To Create An Array In Javascript?




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There are two main ways to create an array in JavaScript.
1. Using An Array Initializer (Array Literal). The array initializer (array literal) syntax is simple. It is a comma-separated list of values in square brackets.

Let's see some examples.


var myArray1 = [1,2,3,4,5]   
// an array with 5 elements
var myArray2 = [5]              
// an array with 1 element 
var myArray3 = [true,'Hi',[7]]  
// element types need 
not be the same.

2. Using The Array Constructor.
The Array constructor method has three different syntaxes. If we call the constructor with two or more arguments, it declares an array with array elements also initialized. If we provide only one argument to the Array constructor, it refers to the length of the new array with, elements not initialized. Lastly, the constructor without any argument creates an array with its length set to zero with elements not initialized.

Let's see some examples.


var myArray4 = new Array(1,2,3,4,5) 
// an array with 5 elements
var myArray5 = new Array(20)    
// an empty array of length 20
var myArray6 = new Array()   
// an empty array of length 0

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4- What Are Javascript Cookies?




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A cookie is a piece of data which is sent from a website (that owns the requested web page) and gets stored locally by the browser at the user end. Cookies are needed because HTTP protocol which arranges for the transfer of web pages to your browser, is stateless. It means that HTTP has no way to keep track of the activities performed by the user at an earlier point in time. One way to resolve this issue is by using cookies. It contains the following data.

* A name-value pair containing the actual data
* An expiry date after which the cookie is no longer valid
* The domain and path of the server it should be sent to
When a request arrives at the server for a web page that maintains a cookie, the server appends the cookie to the HTTP header to send it across. The server-side programs can then read out the information included in it and decide that you have the right to view the page or not and other user preferences. Thus, every time you visit the site that maintains the cookies, your information is available there.

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5- Write a function in ES6 which takes id as argument and find the name based on id




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var findUser = function(id) {
var theData = {
"users": [{
"id": "661", "name": "ford" },
{ "id": "11", "name": "Jama", },
{ "id": "100", "name": "Jay", },
{ "id": "110", "name": "amina",},
{ "id": "120", "name": "Joe",},
{ "id": "1", "name": "cali", },
{ "id": "657", "name": "ruun", },
{ "id": "654", "name": "layla", },
{ "id": "653", "name": "Mj", },
{ "id": "650", "name": "queen", }
]
};
for (var i = 0; i < theData.users.length; i++) {
var user = theData.users[i];
if (user.id === id)
return user.name;
}
}
console.log(findUser("11"));
//output jama

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6- Write javascript code to deeply clone an object.




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Fast cloning with data loss - JSON.parse/stringify
If you do not use Dates, functions, undefined, Infinity, RegExps, Maps, Sets, Blobs, FileLists, ImageDatas, sparse Arrays, Typed Arrays or other complex types within your object,

a very simple one liner to deep clone an object is:
JSON.parse(JSON.stringify(object))

const a = {
string: 'string',
number: 123,
bool: false,
nul: null,
date: new Date(), // stringified
undef: undefined, // lost
inf: Infinity, // forced to 'null'
re: /.*/, // lost }

console.log(a);
console.log(typeof a.date); // Date object
const clone = JSON.parse(JSON.stringify(a));
console.log(clone);
console.log(typeof clone.date);
// result of .toISOString()

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