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C # tutorial
Arrow functions were introduced in ES6
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.
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);
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.
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 |