fix: avoid URL illegal constructor error

[onsclom]

nodeFileTrace errors on const URLParser = typeof window === 'undefined' ? URL : 'b' with TypeError: Class constructor URL cannot be invoked without 'new'.

This is because this code:

async function ConditionalExpression() {
  return {
    test: 'foo',
    then: URL,
    else: 'bar',
  };
}
await ConditionalExpression();

calls URL() since ConditionalExpression is an async function returning a thenable.

Solution: rename all .then fields to .ifTrue since then is reserved for thenables.

Closes #447

[styfle]

This looks wrong. Why would URL always be undefined?

I suspect the root cause is somewhere else since this code represents the ternary from what I can tell.

[TooTallNate]

This will be confusing for future readers. Can we add a comment explaining why the special case here?

[onsclom]

Went with a new (and I think better) solution!

then is reservered for thenables, so changed everything in the code from then -> ifTrue.

[styfle]

Wow, nice catch!