The THIS Keyword In Javascript

I don’t remember I write the first line of JS code how long before from now. It seems like happen every a long time ago, Until now, I still do not know what exactly is this in JS. Too bad, but today I will try to understand it again.

What is THIS?

this is an object in Javascript and object in Javascript like a hash in other language programming.

In a blank file js, if you run one line code blow:

1
console.log(this);

So, what is appear after run? The output will not is an error, just like blow:

1
{}

So, yes, this always exist in Javascript code. I used to believe this only exist in an object or in a function, but it’s not true.

The JavaScript this keyword refers to the object it belongs to. So that is why always exist an this in Javascript.

THIS in Context

This has different values depending on where it is used:

  1. In a method, this refers to the owner object.

  2. Alone, this refers to the global object.

  3. In a function, this refers to the global object.

  4. In a function, in strict mode, this is undefined.

  5. In an event, this refers to the element that received the event.

  6. Methods like call(), and apply() can refer this to any object.

Reference

[1]https://www.w3schools.com/js/js_this.asp

[2]https://developer.mozilla.org/en-US/docs/Glossary/Global_object

[3]https://www.smashingmagazine.com/2014/01/understanding-javascript-function-prototype-bind/