treeshaking with class static field

[StarHosea]

I has a module1, source code is

// index.ts
export class MyTest1 {
  private static instance: MyTest1;

  public static getInstance() {
    if (!MyTest1.instance) {
      MyTest1.instance = new MyTest1(); 
    }
    return MyTest1.instance;
  }
}

export class MyTest2 {}

module2

import { MyTest2 } form 'module1'
console.log(MyTest2)

After packaging module 2, MyTest1 appears in the packaging artifact, which is not actually referenced. Is this the expected performance ?

===
module2 build artifact like this below

var __defProp = Object.defineProperty;
var __defNormalProp = (obj, key, value) => key in obj ? __defProp(obj, key, { enumerable: true, configurable: true, writable: true, value }) : obj[key] = value;
var __publicField = (obj, key, value) => __defNormalProp(obj, key + "", value);
const _MyTest1 = class _MyTest12 {
  static getInstance() {
    if (!_MyTest12.instance) {
      _MyTest12.instance = new _MyTest12();
    }
    return _MyTest12.instance;
  }
};
__publicField(_MyTest1, "instance");
class MyTest2 {
}
console.log(MyTest2);

[rschristian]

Generally, class methods cannot be shaken, no. Certain tools will attempt it but it's quite limited in the scope in which it works.

[StarHosea]

This probably has nothing to do with tree shaking of class methods. In module2, it only imports MyTest2, so MyTest1 should not be included in the bundle.

I tried to change the build output of module1, splitting MyTest1 and MyTest2 into two files and exporting them in index.js like this. Then, tree shaking worked as expected.

module1 build output:

dist/
     index.js 
     MyTest1.js
     MyTest2.js

// index.js
import { MyTest1 } from "./MyTest1.js";
import { MyTest2 } from "./MyTest2.js";
export {
  MyTest1,
  MyTest2
};

module2 build output:

class MyTest2 {
}
console.log(MyTest2);

Now, only MyTest2 is included.

[sapphi-red]

I wasn't able to reproduce: https://stackblitz.com/edit/vitejs-vite-nfpb8a?file=src%2Fmain.ts,src%2Fsub.ts,vite.config.ts&terminal=build

You might be facing these issues (evanw/esbuild#3765, evanw/esbuild#3965), but I'm not sure.

[StarHosea]

Here is a demo : https://stackblitz.com/edit/vitejs-vite-qgbnyf?file=packages%2Fmodule2%2Fsrc%2Findex.ts
@sapphi-red

follow these steps:

pnpm install
pnpm run build

[sapphi-red]

In this case, you are facing the issues I linked above. Setting build.target: 'es2022' on the module1 side would work if you are fine with requiring the library users to transpile the library when using it.

Another way to solve is to write it like so that the injected __publicField won't be treated as a side effect.

export const MyTest1 = /** #__PURE__ */ (() => class MyTest1 {
  private static instance: MyTest1;

  public static getInstance() {
    if (!MyTest1.instance) {
      MyTest1.instance = new MyTest1();
    }
    return MyTest1.instance;
  }
})()

export class MyTest2 {}

[StarHosea]

Thank you for your response; it works