When transform nullish coalescing it transform != null which may lead to wrong result

[IrisChen7]

esbuild version: esbuild node version: 16.20.0

Below is my code

import * as esbuild from 'esbuild'

let ts = 'a = b ?? 1'
let result = await esbuild.transform(ts, {
  target: [
    'es6',
  ],
})
console.log(result.code)

Run result: a = b != null ? b : 1;

Expected result: a = b !== null && a !== undefined ? b : 1;

Since result of 0 ?? 1 is 0, this may lead to wrong result, is there any settings that can make it right?

[hyrious]

a == null is effectively equal to a === null || a === undefined, as the spec of ECMAScript said. So it is a totally correct transform.

$ node -p 'a=0;b=1;a??b'
0

$ node -p 'a=0;b=1;a!=null?a:b'
0

[magic-akari]

The only difference is document.all. If you are using Babel, you can achieve code as concise as esbuild's by set https://babeljs.io/docs/assumptions#nodocumentall.

Apart from document.all, they are equivalent.

It appears that esbuild has adopted this strategy by default.

[evanw]

Yes, the document.all edge case is only the reason why some tools have different output than esbuild here. Specifically document.all is the only value in all of JavaScript for which x != null is false but x !== null && x !== undefined is true.

But it's such an obscure edge case that I have decided I don't care about it. FWIW terser, another popular JavaScript minifier, has also decided that they don't care about document.all either: https://github.com/terser/terser/issues/408.

It's ancient web history and doesn't belong in modern JavaScript code. It's not worth bloating everyone's code by transforming ?? into this double-comparison just to handle the document.all value that no one should be using in the first place.

I'm closing this issue as I won't be changing anything here.

Since result of 0 ?? 1 is 0, this may lead to wrong result, is there any settings that can make it right?

Note that 0 ?? 1 and 0 != null ? 0 : 1 are both 0. So esbuild is correct.