Fix webidl_binder so it can't handle missing assert function

[sbc100]

This can happen when ASSERTIONS is not set and we are in STRICT mode or MINIMAL_RUNTIME mode.

See #20592

[dasa]

Suggested change

	if (typeof assert == "undefined") {
	assert = (cond) => {}
	}
	if (typeof assert === "undefined") {
	var assert = () => {};
	}

[kripken]

This may not work, if the generated code here is in a different scope than where assert is defined,

function assert() { .. }
function other() {
  if (typeof assert === "undefined") {
   // assert is always overridden here
    var assert = () => {};
  }
}

I think the WebIDL binder output here is usually added in a pre-js, so maybe that would be fine. However, it seems a little risky. Might be simplest to just define a new wassert and use that in the WebIDL binder code, perhaps?

[sbc100]

I think the above example would work just fine wouldn't it typeof assert === "undefined" will return false if there is an assert in the output/global scope.

webidl code certainly must be the same scope as the emscripten module code and --post-js is the canonical way to use it.

In the long term I hope to add --debug flag to webidl_binder.py but for now I think this solution should work fine.

[sbc100]

Because JS does function hoisting the check will always work regardless of whether this code comes after of before the assert declartion.

For example the following code always prints "good" regardless of whether it is run at the global scope or in a function:

  if (typeof assert == 'undefined') {
    console.error('oops');
  } else {
    console.error('good');
  }

  function assert() {
  }

[kripken]

I think the above example would work just fine wouldn't it typeof assert === "undefined" will return false if there is an assert in the output/global scope.

No, there is a problem with scoping. Here is an extension of my example that is runnable:

function assert() {
  throw "true assert";
}

function other() {
  if (typeof assert === "undefined") {
    // assert is always overridden here
    var assert = () => {};
  }
  assert(1 == 0);
}

other();

Running that does not throw true assert, showing the assert was always overridden.

var is scoped to the function, so entering other means that the assert in the outer scope does not matter. Just the presence of the var means that assert is equal to undefined in that scope (as it is undefined until it actually reaches the var).