re: Let me explain to you what is `this`. (Javascript) VIEW POST


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); }


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

prints respectively the Window object and the obj one?


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.



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!

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. :)


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

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