ES6

Question 1

Features of es6

Answer 1

• > Let & Const
• > Destructring
• > Templete string
• > Iterators
• > Generators
• > Promises
• > Arrow Functions

Question 2

Difference Between Var & Let & Const

Answer 2

• Var have Global Scope.
• Let and Const have Block Scope.
• const cannot be reinitialize we can use objects to change values in const.

Question 3

Templet Literals

Answer 3

Templet literals are string literals ( ` ` ) allowing combine expressions.
You can use multi-line strings.

Ex : let data= '<h3>hi</h3>
                        <h2>hello</h2>'
{ this will throw error}
new syntax : let data= `<h3>hi</h3>
                        <h2>hello</h2>`

Question 4

String Methods

Answer 4

• indexOf
• lastIndexOf
• search
• slice(-12);
• substring(7, 13);
• replace
• toUpperCase
• concat
• trim
• split

Question 5

Spread operator

Answer 5

• Represented with … 3dots.
• To manipulate array and object
  allows to expand where multiple argumens are expected

Ex
arr1 = [1,2,3] & arr2 = [4,5,6]
arr3 = (…arr1,…arr2)

Question 6

Rest operator

Answer 6

• Accept all number of arguments by …n

- Here n will use as argument inside function.

Question 7

what is Set()

Answer 7

Create a object lets us to store Unique values of any type or objects .

let Myarray = [10,20,30,10]
let myset = new Set(Myarray);

log(myset)//{ 10,20,30 }
myser.add({a:100,b:200})
log(myset)//{ 10,20,30,({a:100,b:200}))

Question 8

Arrow Function

Answer 8

• Introduces in Es6
  its a Shorthand notation for creating Functions
  no need to use “Function” Keyword
• Arrow Function Lexical “This” feature

Question 9

Promises

Answer 9

Promises are used to handle Asynchronous Operations.

promise.then(function (response){ // some code }
.cache(function (error){ // catch Error }
Ex : login with axios

Question 10

difference b/w settimeout and settimeinterval

Answer 10

settimeout : will execute only once after set time.
settimeinterval : will execute again and again after set time.

minimum time for time is 4milliseconds, if u put 0sec it will still take 4milliseconds.

Question 11

data types in js

Answer 11

• number
• string
• object
• boolean
• undefined

Question 12

Js is interpreted or compiled

Answer 12

—- INTERPRETED —–

Interprets each line and run it in browse.
JS is Casesensitive language

Question 13

what is “ This “ Keyword

Answer 13

It refers to object from where it was called.

Question 14

Event Loop

Answer 14

• Event Loop is a queue of call back functions.

- when a a-sync fun is executed all callback function is pushed into queue.

Question 15

Call Stack

Answer 15

It is a data structure for JS interpreter to keep track of all function calls.

for example : fun function is executing then fun1 is called then interpreter will store a pointer in stack and jumps to fun 1 in the fun2 fun3 is called then again interpreter will store a pointer in stack and jumps to fun 3 after completion of fun3 then it will take top most pointer from stack and moves back until stack is empty.

Question 16

What is Hoisting

Answer 16

Its a JS mechanism where variables and functions declaration are moved at top of their scope before executing.

a=1;
log(a+1); //2
var a
-------------------------
log(a+1); // Undefined
a=1;
var a;
For let it will throw error while assigning only.

Question 17

Types of scope

Answer 17

• Block Scope
• Function Scope
• Module Scope
• Global Scope
• Lexical Scope

Question 18

What is Scope

Answer 18

Policy that Manages Accessibility of variable.

Question 19

Lexical Scope

Answer 19

Accessing a variable inside inner function while it is declared in outer function.

Question 20

What is Closure

Answer 20

Creating Function inside another Function.

Inner Function

Question 21

Call, Apply and Bind

Answer 21

Call fun Invokes function passing object in first argument and Then other args seperating by comma.

Example : invite.call( obj, ‘hi’, 123 )

Apply fun Invokes function passing object in first argument and Then other args are sent in array.

Example : invite.call( obj, [‘hi’, “hello”] )

Bind will return new functions and it allows to pass argument.
var inviteemployee = invite.bind(emp)
inviteemployee( 'hi' , 'hello' );

Question 22

Scope Chain

Answer 22

While executing a function, to use a variable it will check for the value of variable inside scope if not found it search outer scope if still not found search in global scope this is called scope chain.

Question 23

IIFE

immediate invoked Function Expression

Answer 23

(IIFE) is js function that runs as soon as it is defined.

• Primary reason to use this function is to obtain data privacy.
• Variables cannot be accessed in iife.

Question 24

Immutable objects

Answer 24

Add Delete Change
Object.Freeze() X X X
Object.seal() X X yes
Object. Prevent-extension() X yes yes

Question 25

Reduce

Answer 25

Execute a reducer Function each value of array resulting single output.

arr = [1,2,3]
const fun1 = ( accumulator.currval ) => { acc + cval }
log(arr.reduce(fun1)) /// 6 [1+2+3]
- We can even pass a initial value.
log(arr.reduce(fun1,1)) /// 7 [1+1+2+3]

Question 26

Event Bubbling

Answer 26

Event bubbling is a type a propagation where the event first trigger the inner most element and then successive trigger parent element.

[][][][][][][][][][]
[][][][][][][]
[][][][][]

• Click on lower event of child automatically parent event also triggered.

Question 27

First-class function

Answer 27

Functions in language is treated like variables by assigning them to variables.

Question 28

First Order Functions

Answer 28

Function does not accept function as arguments or return any function

Question 29

Higher Order Functions

Answer 29

Function accept function as arguments and return function

Question 30

Asynchronous

Answer 30

Js is single threaded programing i,e only one thing will happen at a time

Using asynchronous we can perform long network request without blocking the main thread

• Promises
• Call Back
• Async / Await

Question 31

Object Functions

Answer 31

Object.assign() : Copies the values.
Object.create() : Creates a new object.
Object.values() : Returns an array containing the values that correspond to all of a given object’s own enumerable string properties.
Object.keys()
Returns an array containing the names of all of the given object’s own enumerable string properties.

Object.freeze()
Object.isFrozen()
Object.seal()
Object.isSealed()
Object.preventExtensions()
Object.isExtensible()