Dead code not eliminated

[jaydenseric]

With this code in in.js:

if (0 && false) console.error('abcde');

And this use of the CLI:

esbuild in.js --bundle --minify --outfile=out.js

abcde correctly does not appear in the out.js bundle.

But, unexpectedly, it does with this:

if ((0 + 0) && false) console.error('abcde');

In real world modules, I have code like this:

if (typeof process === 'object' && process.env.NODE_ENV !== 'production') {
  Foo.displayName = 'Foo';
  Foo.propTypes = {
    className: PropTypes.string,
    children: PropTypes.node.isRequired,
  };
}

The idea is, when process.env.NODE_ENV is 'production', the React component displayName and propTypes should be dead-code eliminated from the bundle. This works with webpack but not esbuild.

With this CLI usage:

esbuild in.js --bundle --minify define:process.env.NODE_ENV=\"production\" --outfile=out.js

The process.env.NODE_ENV !== 'production' is swapped with false in the out.js bundle, but the dead code is not eliminated.

[evanw]

Thanks for the report. I have a substitution rule for false && anything → false but it looks like I also need a rule for noSideEffects && false → falsy.

[jaydenseric]

Great, thanks for the speedy response :)

Even if the left side of the if condition has side effects, the if block could be eliminated.

For example this:

if (foo() && false) {
  console.log('abcde');
}

Could become:

foo();