JavaScript Arrow Function
Arrow functions were introduced in ES6.
Arrow functions allow us to write shorter function syntax:
let myFunction = (a, b) => a * b;
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:
Note: This works only if the function has only one statement.
If you have parameters, you pass them inside the parentheses:
In fact, if you have only one parameter, you can skip the parentheses as well:
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);
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);
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 |