Unbound function context in JavaScript

Let's see what happens if you specify this in the function not bound to any element, like this:

function func() { console.log(this); } func();

In this case, the result depends on whether we have a strict mode or not. If the mode is non-strict, then this will store a reference to window:

function func() { console.log(this); // reference to the window } func();

And if the mode is strict, then undefined will be stored in this:

"use strict"; function func() { console.log(this); // undefined } func();


From the above it would seem that in strict mode this will always be undefined. It's not the case! If you just output this outside the function, then it will have a reference to window regardless of the mode:

"use strict"; console.log(this); // there is reference to the window in this

Let's summarize

You can write this in any function without causing any JavaScript errors. But what exactly will lie in this is not defined until the moment the function is called. Moreover, with different function calls, this can be different values. It all depends on the context in which the function was called.