Preconstruct strips out browser env check for .browser.{cjs, esm}.js build files

[ajimae]

Issue:

In snippet.ts I have the following snippet which checks for browser environment.

// snippet.ts
const isBrowser = () =>
  typeof window !== 'undefined' &&
  window.document &&
  window.document.nodeType === 9

In the build files snippet.browser.cjs.js and snippet.browser.esm.js the above snippet is transpiled into:

// snippet.browser.cjs.js or snippet.browser.esm.js
const isBrowser = () =>
  window.document &&
  window.document.nodeType === 9

stripping out the typeof window !== 'undefined' check.

However, in the build files snippet.cjs.js and snippet.esm.js the above snippet is transpiled into:

// snippet.cjs.js or snippet.esm.js
const isBrowser = () =>
  typeof window !== 'undefined' &&
  window.document &&
  window.document.nodeType === 9

as expected.

Expected behaviour:

This very check typeof window !== 'undefined' should not be stripped out of the *.broswer.cjs.js and *.browser.esm.js build files.

Question:

• Why is this the behaviour?
• Is there a way to prevent this?

[emmatown]

Replacing typeof window with "object" and dead code elimination from that is the entire behavior of the browser builds, if you'd like to avoid it, you can avoid generating browser builds and use the general builds in browsers.