Javascript: Extend Classes With Undefined Class

Consider the following two files: /* file A.js */ class A extends B { } /* file B.js */ class B { } If I accidentaly load these two files into the browser in the inverse order

Solution 1:

I'd resolve it by using modules. Modules declare their dependencies explicitly and you only have to reference the top-level module in the page; the rest will be loaded according to the dependency tree. So for instance, B.js would be:

exportclassB {
    // ...
}

Then A.js would be:

import { B } from"./B.js";
exportclassAextendsB {
    // ...
}

Perhaps your main entry point (main.js or whatever) would have:

import { A } from"./A.js";
// ...

Then your page has

<scripttype="module"src="./main.js"></script>

...and the other dependencies are loaded as needed.

This works with native module support in browsers, and/or if you use a bundler like Rollup.js, Webpack, ...