NOTE: This tool should only be used on packages in this repository, and is not intended for external usage.

This tool rewrites TypeScript-compiled JavaScript files in the current directory to make all subpackage imports lazy. Subpackages will only be imported when they are actually used/needed, instead of all packages being all read on startup.

This can be used to reduce the load time of large JavaScript libraries, large parts of which may go unused in any particular client application.

# Run on all JavaScript in the current directory
lazify .

We apply the following transformations:

We turn this:

const my_module_1 = require('./my-module');

function hello() {
  return my_module_1.hello();
}

Into this:

function my_module_1() {
  return require('./my-module');
}

function hello() {
  return my_module_1().hello();
}

This makes it so my-module.js is only loaded if and when the hello() function is actually called. If that function is never called, we didn't need to needlessly load my-module.js.

The following TypeScript idiom:

export * from './my-module';

Is hard to make lazy, because it requires knowing the symbols that are available in my-module.

What this package does is load my-module.js at transform time, inspect its list of exported symbols, and make a list of lazy getters for each of those symbols.

So, after statically determining the list of symbols to be foo, bar and baz, the above gets turned into:

Object.defineProperty(exports, "foo", { get: () => require("./my-module").foo });
Object.defineProperty(exports, "bar", { get: () => require("./my-module").bar });
Object.defineProperty(exports, "baz", { get: () => require("./my-module").baz });