Deno•11mo ago

How to initialize global variable so it can be accessed without globalThis?

I'm hacking on a large existing codebase using Deno. This codebase uses a number of global variables like this:

if( __DEV__ && ... )

if( __DEV__ && ... )

Their build system sets these values at build time I think. I am trying to hack around without building, but I am stuck because I haven't figured out how to initialize these variables globally. I always get an error of "ReferenceError DEV is not defined".

The code I'm working with uses ESM modules and TypeScript. There is a global.d.ts that sets

declare var __DEV__: boolean

declare var __DEV__: boolean

I include this global.d.ts via deno.json:

"compilerOptions": {
        "types": [
            "./global.d.ts"
        ]
    },

"compilerOptions": {
        "types": [
            "./global.d.ts"
        ]
    },

This makes the TS side of things happy. But I still don't know how to actually initialize that value. I tried globalThis, window, and just DEV = true;

Any help would be appreciated, thanks!

teleclimberOP•2/1/25, 10:02 PM

I think I figured it out. Or at least I found a way to make it work, even if I don't understand why it works.

teleclimberOP•2/1/25, 10:03 PM

I have to initialize the values in a separate file, using globalThis:

teleclimberOP•2/1/25, 10:05 PM

And then import that file from my index.js entrypoint. works from a file that is imported, but it doesn't work if I type the exact same thing in my index.ts.

teleclimberOP•2/1/25, 10:05 PM

So I got it working, but if someone wants to explain enlighten me as to what's going on here I'm all ears.

marvinh.•2/4/25, 10:19 AM

When you do

then what's actually happening is

In other words: All global variables hang off of the object. That's the object that holds the global scope.

teleclimberOP•2/6/25, 6:56 PM

OK but that doesn't explain why doing from the main script has no effect.

marvinh.•2/6/25, 10:26 PM

Where are you putting that line? Are you putting it before or after imports of other modules?