What does ReturnIfAbrupt mean in ES6 draft?

Question

I\'m currently implementing some shims for the ES6 draft. I\'m wondering if anyone can tell me what ReturnIfAbrupt means. For instance, my implementation for

Answer 1

ReturnIfAbrupt is referring to an Abrupt Completion. A completion record contains a type and the value associated with it. A normal completion would be something like an expression's resulting value. A return completion from a function is the usual expected completion aside from a normal completion. Any other completion types are abrupt. That's throw, break, continue.

if (isCompletionRecord(v)) {
  if (isAbruptCompletion(v)) {
    return v;
  } else {
    v = v.value;
  }
}

Implementing it as you are, what it would entail is wrapping the function in a try catch. A thrown value would be an abrupt completion. This isn't something you see at the JS level though, it's for implementing control flow and non-local control transfers at the engine level.

I've implemented much of the ES6 spec in a JS virtual machine that may also help shed some light on it, here's ToInteger: https://github.com/Benvie/continuum/blob/master/lib/continuum.js#L516

function ToInteger(argument){
  if (argument && typeof argument === OBJECT && argument.IsCompletion) {
    if (argument.IsAbruptCompletion) {
      return argument;
    }
    argument = argument.value;
  }
  return ToNumber(argument) | 0;
}