Is 'use strict' necessary?

[Rastersoft]

Is it still necessary to add “use strict”; in a GJS script, like an extension or a program, or today any code is already run in strict mode “automagically”?

[andyholmes]

I believe if you’re using ESM, this is non-optional (i.e. it is turned on automatically). Otherwise, it can make a difference, but these days they’re generally obvious mistakes.

For example, if you use 'use strict'; with the code below, you will get a critical warning and throw an exception, otherwise you will get a global variable:

// 'use strict';

function foo() {
  bar = 'baz';
}

[fmuellner (Florian Müllner)]

@andyholmes

I believe if you’re using ESM, this is non-optional (i.e. it is turned on automatically).

Yes, and it’s the same for class bodies. That is, most code should already be covered before porting to ESM.

[Rastersoft]

@andyholmes @fmuellner No, no… You didn’t understand. My question is: do I still have (as of December, 2022) to write “use strict” at the beginning of all of my javascript files, when writing a GJS/GTK application, to get all the bells and whistles of the strict mode? Or is it automatically enabled in all programs, and it is only required in web pages?

[fmuellner (Florian Müllner)]

The short answer is: Yes if you use gjs’ legacy imports, no if you use modules.

[sonny (Sonny Piers)]

Simply put; yes you need ‘use stict’ unless the program started with gjs -m (ES modules)