Dynamic import(): how to ignore an import that’s passed a variable?

[iamakulov]

In our codebase, there’re a few cases where we deliberately use a native import() with a variable, like:

for (const moduleName of moduleNames) {
    const evaluationResult = await import(/* webpackIgnore: true */ moduleName)
    this.evaluatedModules[moduleName] = evaluationResult
}

This works in webpack thanks to /* webpackIgnore: true */ (docs). But in ESBuild, this produces a warning like:

xxx/xxx.ts:241:47: warning: This dynamic import will not be bundled because the argument is not a string literal

Is there any way to silence this warning for such import? If this was a string literal, I’d add it into externals, but I can’t do that with a variable.

[evanw]

This is a general problem with warnings in esbuild. Currently there isn't a built-in way to filter specific warnings. Some options:

1. You could use --log-level=error to silence all warnings.

2. You could filter warnings yourself using the API.

3. I currently skip similar warnings for require() when inside a try block, since presumably that is evidence that the code is anticipating possible errors and can handle them correctly. I should probably do that for this await import() pattern too.

4. I could just remove this warning entirely. Arguably import() returns a promise that could be rejected, so code that uses it should be handling that failure anyway. However, this is likely to cause confusion when esbuild silently succeeds but the resulting bundle doesn't work. Also anecdotally I have never seen real code that uses import() and actually handles errors, so these failures would likely be silently ignored. This doesn't seem great.

5. I could keep the warning. Warnings exist to point out potential issues and don't cause the build to fail. Arguably this warning is working correctly.

[iamakulov]

Thank you, that makes sense! I agree that this warning seems totally reasonable (and FWIW the code isn’t handling import() errors in that case properly either). I’m going to try 1 or 2, then.