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Making Arrow in Javascript - ES 6

Arrow function aka fat arrrow was intorduced in ES6 as a new syntax for writing Javascript function.This is the most popular and highly used ES6 feature. Source Ponyfoo
What is Arrow function? Arrow functions provide a different way of creating functions in JavaScript. Besides a shorter syntax, they offer advantages when it comes to keeping the scope of the this keyword. What I meant by this line is, unlike other functions, the value of this inside arrow functions is not dependent on how they are invoked or how they are defined.It depends only on its enclosing context.
// ES5 - function declaration function callMe(name){              console.log(name);  }
which you could also write as:  // ES5 - function expression
const callMe = function(name) {         console.log(name);
}
becomes:  // ES6
const callMe = (name) => {              console.log(name);  }
Important Uses:When having no arguments, you have to use empty parentheses in the function declaration:
const callMe = () => {

How to Spread in Javascript - ES 6

Spread syntax was introduced as part of Javascript in the ES2015/ECMAS-6.

This allows iterable likes array, object or string to get expanded.

Spread can be used in following ways:
in array : [...iterableArray, 3 , 'four', 5]
in object : {...iterableObj}

The spread operator is very useful for concat, copying,apply, expanding, math operations,etc in array and objects. Let discuss each in detail.

Concat
var arr1 = [1,2,3];
var arr2 = [4,5,6];

without spread
var concatenatedArray = arr1.concat(arr2); // [1,2,3,4,5,6]

with spread
var concatenatedArray = [...arr1, ...arr2 ] // [1,2,3,4,5,6]

Copying
var arr1 = [1,2,3];
var arr2 = [...arr1];
arr2.push(4);
console.log(arr2); // [1,2,3,4]
console.log(arr1); // [1,2,3]

Replacement for apply
var add = (a,b,c) => a+b+c;
var arr1 = [1,2,3];
add(...arr1); // replacing add.apply(null,arr1);

Expanding array
var programming = ["Java", "NodeJs", "Python"];
var subjects = ["Physics", ...programmi…

Javascript Interview Question and Answer - 3

In this post, I have discussed 5 basic javascript question and answer that is mostly asked in the interviews. Most of the time interviewer starts the interview with some of these basic questions.
So here we have

Q1. What is the difference between == and ===?

Solution : When we want to test the equality of two values(LHS and RHS), we use == or ===.
== is basically used to check if the two values are equal or not,and we are not considering their datatype. e.g.
if we check

5 == "5"   // true as values are equal
undefined = null   //  true as both represents NO VALUE

In case of ===, we not only consider the values but the datatype as well.e.g.

5 === "5"   // false as though values are equal but datatypes are different

Similarly

undefined === null  //  false, as datatype of undefined and null is undefined and object respectively

It is highly recommended to use === in the programming as we get very unexpected results out of ==. e.g.

false == 0   // true
false == "false&qu…

Javascript Interview Question and Answer - 1

In this article we are going to discuss 2 javascript interview question and their answers.These questions are highly asked in the Javascript interviews.

Disclaimer: - You might have different solution working with all test cases for both the problems.

So lets discuss the first question.This question is to test your ability in terms javascript object knowledge and your logical thinking.

Q1. You have been given a nested object "Person" which has one of the property as "password".Write a generic function to change the value of all the "password" property to "*****". Object is nested and may contain other object with property "password" and so on. Here is a sample object.

var Person = {
     name: 'Alex',
     age : 40,
    password : 'abc',
    x : {
       name : 'Chris',
       password: 'abcd',
       y : {
          name : 'Mike',
          password: 'abcd',
         },
     }
.
.
}

Before we …

Difference between undefined and null

Today we are gonna talk about the famous question in Javascript which all of us must have faced in interview.

The difference between undefined and null.

But before we talk about their differences, lets first think, why are we comparing undefined and null and why not undefined and string or string and null?

So there must be something common,in general, between undefined and null. And that commonality is both of have them represents NO VALUE for the variable.

You can also call this NO VALUE as void or empty.

So basically when we say as variable is undefined or null that mean the value doesn't exist for the variable. Lets see how is it so.

1.   undefined == null     // true, so the value is same

Now lets check each one of them.First lets talk about undefined.

When do we get this undefined? Generally when we declare a variable but doesn't initialise it we get undefined. e.g

1.   var foo;
2.   console.log(foo);   // undefined

Also when we try to access a variable before its initialis…

Difference between var, let and const

var, let and const in Javascript
 Variable can be declared in three ways: varletconstvar variables are function-wide scoped. Let's understand this with an example,    if(true){
      var x = 5;    // variable declared with "var"         console.log(x);  // x will be 5
   }
 console.log(x); // even here, x will be 5 
So in the last example we can see variable "x" is available outside the "if" block, that means the scope of variable with "var" is not block scope.
let see with another example,
1.  function helloWorld(){      var x = 5;
2.     function abc(){
3.        console.log(x);      // even x will be 5
4.     }
5.     abc();
6.     console.log(x);  // x will be 5
7. }
8. helloWorld(); So in this example, we can see the variable "x" is available throughout the function in which it is declared.
One of the famous example/question discussed in the interviews is following
1.       for(var i=0;i<5;i++){
2.                console.log(i);
3.       }
4.…