add jsconfig support

[viankakrisna]

No description provided.

[evanw]

Thanks for taking a stab at this.

I haven't used jsconfig.json before and I'd like to understand it better if esbuild is going to support it. Right now I can't figure out how to test it. According to the documentation jsconfig.json is supposed to be just like tsconfig.json except with the "allowJs" attribute set to true, but I am unable to confirm this.

tsconfig.json

I understand how tsconfig.json works. You can test whether or not tsconfig.json has an effect by configuring the module property, which affects the generated JavaScript. For example, if I make a tsconfig.json file like this:

{ "compilerOptions": { "module": "amd" } }

And then compile this foo.ts file by running tsc:

import * as fs from 'fs'
console.log(fs)

I get the following JavaScript file:

define(["require", "exports", "fs"], function (require, exports, fs) {
    "use strict";
    Object.defineProperty(exports, "__esModule", { value: true });
    console.log(fs);
});

It uses AMD so I can tell that the TypeScript compiler is actually reading tsconfig.json.

jsconfig.json

I tried the same thing with jsconfig.json. I made this jsconfig.json file:

{ "compilerOptions": { "module": "amd" } }

And this foo.js file:

import * as fs from 'fs'
console.log(fs)

Then I tried to invoke the TypeScript compiler such that it picks up the settings in jsconfig.json. I wasn't able to do this though. Here's what I tried:

# This generates JavaScript in CommonJS format,
# not AMD format (so jsconfig.json was ignored)
tsc --outDir out --allowJs foo.js

# This doesn't generate any output files at all
tsc --outDir out --project jsconfig.json

Can you help me understand how jsconfig.json works? I'd like to understand how and when the TypeScript compiler parses that file.

[viankakrisna]

From what I observe, jsconfig is usually only used to define paths and resolve mechanism for user space modules in js only project so vscode/supported compiler can know about the custom module resolution. This is the configuration that's honored by Create React App and several other compiler. AFAIK, no other compiler honor anything other than baseUrl and paths for compilerOptions for js files.

Probably you still need --allowJs ?

tsc --outDir out --project jsconfig.json --allowJs

EDIT: looks like it does not produce output files because there are no .ts file in the directory 🤔

this line from docs

jsconfig.json is tsconfig.json with "allowJs" attribute set to true

is probably a convention only used in vscode to run typecheck on js only project with --allowJs

as per now, esbuild only support baseUrl in a tsconfig file, so we can set up module resolution even in a js only project, which is weird because that breaks expectation, new member on the project probably thought that the project is written in TS by the existence of tsconfig in the root folder, while in fact we only use it for setting up baseUrl