--tsconfig= option not working and question of lower case es vs ES

[David-Else]

tsconfig not read

I can type npx esbuild --bundle --tsconfig=nonsense src/mod.ts and it just seems to ignore the nonsense.

If I type npx esbuild --bundle --tsconfig=./tsconfig.json src/mod.ts which should be correct, it ignores the target property, or it is just not reading it at all.

If I corrupt my tsconfig.json and type npx esbuild --bundle src/mod.ts it works, so it is not reading tsconfig.json by default?

es vs ES

In tsconfig.json the target string starts with uppercase ES, for example:

"target": "ES2019",

The hover over in VS Code says:

Specify ECMAScript target version: 'ES3', 'ES5', 'ES6'/'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019', 'ES2020', 'ESNext'

but esbuild wants lowercase es2017 etc? Is there a reason for this? When using https://github.com/egoist/rollup-plugin-esbuild it will only accept lowercase version in the tsconfig.json

I am running Linux.

[evanw]

Some settings are taken from tsconfig.json but esbuild is not a perfect replica of tsc and isn't intended to be.

The target property in tsconfig.json is actually completely ignored by esbuild. Instead, esbuild has its own target property that behaves differently. This has been requested in the past too: #277. I don't think it's a good idea to respect target in tsconfig.json because esbuild supports multiple tsconfig.json files per build but the language target only makes sense as a single value that is a constant for the entire build.

The values for esbuild's target are different than the values for the TypeScript compiler. For example, you can pass node10 or firefox50 to be compatible with those specific versions of those JavaScript environments. So the fact that they are lowercase is an independent decision that's not related to the TypeScript compiler (all of esbuild's flag values are lowercase).

It looks like I'm missing an error for if the file passed to --tsconfig doesn't exist. I'll make that an error.

[evanw]

FWIW this ended up being changed after all. See #1718.