Where to put custom JavaScript? `resources/js/app.js` doesn't seem to work?

I'm trying to add some custom js in my

app.js

app.js

file but it doesn't seem to load. I'm running

npm run build

npm run build

after to be sure and still nothing. Even something as simple as

console.log('Hello, World!');

console.log('Hello, World!');

isn't showing in the console.

I do have a custom theme file but this is just for style overrides right? Or do I need to do something for JS too?

To be more specific, I'm trying to enable chart.js auto colors: https://www.chartjs.org/docs/latest/general/colors.html#default-color-palette

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