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JavaScript Arrow Function


Arrow functions were introduced in ES6.
Arrow functions allow us to write shorter function syntax:


let myFunction = (a, b) => a * b;


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Before Arrow:

hello = function() {  return "Hello World!";}

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With Arrow Function:

hello = () => {  return "Hello World!";}

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It gets shorter! If the function has only one statement, and the statement
returns a value, you can remove the brackets and the
return keyword:

Arrow Functions Return Value by Default:

hello = () => "Hello World!";

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Note: This works only if the function has only one
statement.

If you have parameters, you pass them inside the parentheses:

Arrow Function With Parameters:

hello = (val) => "Hello " + val;

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In fact, if you have only one parameter, you can skip the parentheses as well:

Arrow Function Without Parentheses:

hello = val => "Hello " + val;
this

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What About this?
The handling of this is also different in arrow functions compared to regular
functions.
In short, with arrow functions there are no binding of
this.
In regular functions the this keyword represented the object that called the
function, which could be the window, the document, a button or whatever.
With arrow functions the this keyword always represents the
object that
defined the arrow function.
Let us take a look at two examples to understand the difference.
Both examples call a method twice, first when the page loads, and once again
when the user clicks a button.
The first example uses a regular function, and the second example uses an
arrow function.
The result shows that the first example returns two different objects (window and button),
and the
second example returns the window object twice, because the window object is the
"owner" of the function.

Example
With a regular function this represents the
object that calls the function:

// Regular Function:hello = function() {  document.getElementById("demo").innerHTML
+= this;}// The window object calls the function:
window.addEventListener("load", hello);// A button object calls the
function:document.getElementById("btn").addEventListener("click", hello);

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Example
With an arrow function this represents the
owner of the function:

// Arrow Function:hello = () => {  document.getElementById("demo").innerHTML
+= this;}// The window object calls the function:
window.addEventListener("load", hello);// A button object calls the
function:document.getElementById("btn").addEventListener("click", hello);

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Remember these differences when you are working with functions. Sometimes the
behavior of regular functions is what you want, if not, use arrow functions.

Browser Support
The following table defines the first browser versions with full support for
Arrow Functions in JavaScript:










Chrome 45
Edge 12
Firefox 22
Safari 10
Opera 32


Sep, 2015
Jul, 2015
May, 2013
Sep, 2016
Sep, 2015















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Reference: https://www.w3schools.com/js/js_arrow_function.asp