Feature Request: Annotate keys in __publicField() for mangling compatibility

[mckravchyk]

When targeting ES2017, ESBuild will output public class fields like:

__publicField(this, "propName")

I am using Terser for post-processing with property mangling by Regex enabled. Terser is not able to recognise the string in the function argument as a property to mangle, which makes it incompatible.

The same could be achieved with:

__publicField(this, { propName: '' })

at a small cost of being more verbose and some runtime footprint to get Object.keys(arg)[0] It could be an option / not enabled by default.

Alternatively, is there a reason why Object.defineProperty is not used? This is something that Terser makes an exception for, TypeScript also outputs JS this way.

[evanw]

I think the missing thing for Terser (and for subsequent esbuild runs with --mangle-props) is the addition of a /* @__KEY__ */ comment to annotate the string literals as property keys. Both Terser and esbuild already have a feature where you can annotate strings with /* @__KEY__ */. That change would look like this:

 var __defProp = Object.defineProperty;
 var __defNormalProp = (obj, key, value) => key in obj ? __defProp(obj, key, { enumerable: true, configurable: true, writable: true, value }) : obj[key] = value;
 var __publicField = (obj, key, value) => __defNormalProp(obj, typeof key !== "symbol" ? key + "" : key, value);
 class Foo {
   constructor(it) {
-    __publicField(this, "foo", 123);
-    __publicField(this, "bar");
+    __publicField(this, /* @__KEY__ */ "foo", 123);
+    __publicField(this, /* @__KEY__ */ "bar");
     this.bar = it;
   }
 }
 const { foo, bar } = new Foo(null);
 console.log(foo, bar);

Alternatively, is there a reason why Object.defineProperty is not used? This is something that Terser makes an exception for, TypeScript also outputs JS this way.

Calling Object.defineProperty instead of using a helper function has non-trivial run-time overhead. It makes the generated code both download and run more slowly.

Edit: Compare without the comment to with the comment (the original code is here).

[mckravchyk]

Thanks! Yes, I confirm Terser handles the annotation.