define and boolean elimination

[Conaclos]

Hi!

I would like to thank you again for esbuild and its excellent documentation (including the CHANGELOG).

I use esbuild as the main tool to build my libraries. Usually I have two builds:

• a debug/test build
• a production build (the published one)

In my code I generally extensively use assertions (pre- and post- conditions). I would like to remove these assertions in the production build. The only way I know to achieve it with esbuild is to use a constant such as DEBUG:

// @filename index.js
import { assert } from "assert-mod"
export function sqrt(x) {
  DEBUG && assert(x >= 0);
  return Math.sqrt(x);
}

and set DEBUG to false (or 0) for the production build:

esbuild --bundle index.js --define:DEBUG=false --format=esm --external:assert-mod

However, esbuild emits the following code:

import { assert } from "assert-mod";
function sqrt(x) {
  false;
  return Math.sqrt(x);
}
export {
  sqrt
};

Note the apparition of an expression-statement false;.

Do you think it could be possible to improve a bit the dead-code elimination in order to remove also the boolean constant? The emitted code could be:

function sqrt(x) {
  return Math.sqrt(x);
}
export {
  sqrt
};

Note that I would like to avoid minification to keep a readable code.

Alternative solution

Another solution could be to add a --drop:assert.

[evanw]

The emitted code could be:

function sqrt(x) {
  return Math.sqrt(x);
}
export {
  sqrt
};

No. The external import of assert-mod must be kept because it may have side effects. Dropping that import would be incorrect.

[Conaclos]

@evanw

Ah yes I forgot to add the import. However, it is not the proposal of the issue: the proposal is to remove the useless boolean constant.

In other words, instead of emitting:

import { assert } from "assert-mod";
function sqrt(x) {
  false;
  return Math.sqrt(x);
}
export {
  sqrt
};

esbuild could emit:

import { assert } from "assert-mod";
function sqrt(x) {
  return Math.sqrt(x);
}
export {
  sqrt
};

Diff between the two versions:

import { assert } from "assert-mod";
function sqrt(x) {
-  false;
  return Math.sqrt(x);
}
export {
  sqrt
};

[Conaclos]

Thanks!