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What are arrow functions?

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Arrow functions were introduced in the ES6 version of javascript.

They provide us with a new and shorter syntax for declaring functions.

Arrow functions can only be used as a function expression.

Let’s compare the normal function declaration and the arrow function declaration in detail:

// Traditional Function Expression

var add = function(a,b){

  return a + b;


// Arrow Function Expression

var arrowAdd = (a,b) => a + b;

Arrow functions are declared without the function keyword. If there is only one returning expression then we don’t need to use the return keyword as well in an arrow function as shown in the example above. Also, for functions having just one line of code, curly braces { } can be omitted.

// Traditional function expression

var multiplyBy2 = function(num){

  return num * 2;


// Arrow function expression

var arrowMultiplyBy2 = num => num * 2;

If the function takes in only one argument, then the parenthesis () around the parameter can be omitted as shown in the code above.

var obj1 = {

  valueOfThis: function(){

    return this;



var obj2 = {

  valueOfThis: ()=>{

    return this;



obj1.valueOfThis(); // Will return the object obj1

obj2.valueOfThis(); // Will return window/global object

The biggest difference between the traditional function expression and the arrow function, is the handling of the this keyword.

By general definition, the this keyword always refers to the object that is calling the function.

As you can see in the code above, obj1.valueOfThis() returns obj1, since this keyword refers to the object calling the function.

In the arrow functions, there is no binding of the this keyword.

The this keyword inside an arrow function, does not refer to the object calling it. It rather inherits its value from the parent scope which is the window object in this case.

Therefore, in the code above, obj2.valueOfThis() returns the window object.

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