in-operator broken; `"property" in object` ALWAYS gets inlined as true

Bug report

What is the current behavior?

Webpack v5 incorrectly evaluates & bundles "property" in object as true, when object imported from a different file, even if the property is not present in the object (e.g. "doesNotExist" in { }).

If the current behavior is a bug, please provide the steps to reproduce.

create the following files (e.g. in an empty src folder):

// testObject.js
export const testObject = {}

// main.js
import { testObject } from './testObject'
console.log('property' in testObject ? 'buggy' : 'not buggy')

With or without a webpack configuration, run webpack (e.g. npx webpack-cli). Inspect the emitted bundle. (below: without a configuration file)

// main.js (NODE_ENV=production)
!function(){"use strict";console.log("buggy")}();

// main.js (NODE_ENV=development)
... console.log(true ? 'buggy' : 'not buggy') ...

What is the expected behavior?

The expression 'property' in testObject should evaluate to false, or be evaluated at runtime.

For comparison, with webpack v4 or when using terser directly, I get

console.log("property"in{}?"buggy":"not buggy")}

Workarounds:

The issue does not appear / can be worked around if testObject is defined within the same file or if it’s indirectly referenced. The following three examples work correctly:

import { testObject } from './testObject'
console.log('property' in (0, testObject) ? 'buggy' : 'not buggy')  // => not buggy

const indirectReference = testObject
console.log('property' in indirectReference ? 'buggy' : 'not buggy')  // => not buggy

const testObject2 = {}
console.log('property' in testObject2 ? 'buggy' : 'not buggy')  // => not buggy

Other relevant information: webpack version: 5.71.0 Node.js version: v16.14.0 Operating System: Windows 10

This appears to be the root of https://github.com/chakra-ui/chakra-ui/issues/5804 and https://github.com/chakra-ui/chakra-ui/issues/5812, where currently downgrading to webpack v4 (by downgrading react-scripts) is suggested as a workaround.

[Quovadisqc]

Might help someone that also have the same issue as I had but this also breaks Socket-io by making connections throw timeouts because of this this function

[vankop]

yeah, please use webpack@5.70 for now…