[Plugin] onEnd callbacks modify the build result

[yanm1ng]

I used end callback to modify the build result，it works，but I can't return the new result。

function myPlugin(): Plugin {
  return {
    name: 'my-plugin',
    setup(build: PluginBuild) {
      const options = build.initialOptions;
      options.write = false;

      build.onEnd(async ({ errors, outputFiles }) => {
        if (!errors.length && outputFiles?.length) {
          await Promise.all(outputFiles.map(async file => {
                // some logic to modify output contents...
          }));
        } else {
          console.error(errors);
        }
      });
    },
  };
}

const result = await esbuild({
      entryPoints: [ path.join(__dirname, './entry.js')],
      outdir: path.join(__dirname, 'dist'),
      plugins: [ myPlugin() ]
});

for (let out of result.outputFiles) {
     // still original build result
     console.log(out.path, out.text);
}

also onEnd function type only support void or Promise<void>

[evanw]

Well text is a lazily-evaluated getter instead of a normal property so you have to use Object.defineProperty(file, 'text', { value: 'something' }) instead of file.text = 'something' but changing it should work fine (I just tried it myself). You can also just mutate the outputFiles property on the result argument directly instead if you want. The onEnd callback doesn't have a return value because the result object is provided as an argument and you can fully modify any aspect of it before you return it.

[yanm1ng]

I also found text is a getter before you reply. I will try to modify the result object.
Thank you for your reply anyway ❤️

[eric-hemasystems]

FYI. For anybody that comes across this in the future.

I wasn't able to modify my build result by updating the text property (even using Object.defineProperty(file, 'text', { value: 'something' })). But I could do so by modifying the contents property (this also implicitly modifies text since it is a function that reads from contents). Example:

build.onEnd((result) => {
  const js = result.outputFiles.find(f => f.path.match(/\.js$/))
  const modified = doSomething(js.text)
  js.contents = Buffer.from(modified)
})

To see a fuller example (where I use it to instrument for code coverage) see marvinhagemeister/karma-esbuild#33 (comment)