Discussion on: Let me explain to you what is `this`. (Javascript)

[Elarcis]

this in the body of f is undefined!!! not obj!!!

Why does it happen though, that this code ran on Firefox (and I suppose, any other browser):

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

f();

const obj = {};
obj.fn = f;
obj.fn();

prints respectively the Window object and the obj one?

[YCM Jason]

Great question. You are getting Window because you are not using 'use strict'.

Go to this link and the section called "Securing JavaScript" explains it.

developer.mozilla.org/en-US/docs/W...

[Elarcis]

Oops. That actually explains a lot, as I used to get could not read property 'foo' of undefined a lot when passing my functions around as references, in strict mode.

Thank you for the link, I had forgot how much use strict mode changes the game!

[YCM Jason]

It makes code a little bit more reasonable.

Babel has implicit strict mode and u don't have to worry about forgetting to add it. :)

[Guillaume Martigny]

Without specific definition, this is the object wrapping the function. window is the fallback when can't be infer from any context.

[yahyaoui-mohamed]

To get undefined as result you have to use the strict mode.