Discuss
  • Using Generators in Extended Mode for Co-Routines

Using Generators in Extended Mode for Co-Routines

# Carl Smith (11 years ago)

It seems that ES6 will allow implicit opt-in for generators, with the body of the generator being ES6, so it can yield. It also seems that the plan is that the body would be forced into strict mode.

The following currently works in Chrome with Experimental JavaScript Features enabled, but would not work in strict mode, as the eval call wouldn't execute in the callee's namespace.

function * realm(input) {
    while (true) {
        input = yield eval(input);
    }
}

var r = realm();
r.next();
r.next("var a = 1");
r.next("console.log(a)");

The above functionality is required in an application I'm currently working on, and there's a few features that would use it. There's actually a large class of applications that could do so. I'm essentially doing a REPL, and REPLs are impossible to implement in strict mode. Any app that allows the user to enter code that'll be executed, needs to evaluate source strings in a persistent namespace. If that namespace is not window, then the eval call must live in a scope that can yield flow without destroying its local namespace.

Lots of applications could use this ~ web shells, programming lessons and games, as well as anything that allows the user to script it.

Is there a story for this kind of application, beyond use V8 and hope nothing ever changes?

# Erik Arvidsson (11 years ago)

Generators are not implicit strict. Only modules and classes are.

# Till Schneidereit (11 years ago)

Which is why the example works nicely in Firefox, too.

# Carl Smith (11 years ago)

Thanks. Appreciated. I was led to believe this would change. My bad.