Simple "generator + promise" runner routine. Write sync - execute async.

generator_runner.js

function r(genFn, context){
  return function(...args){
    const iter = genFn.apply(context || this, args);
    return traverse(iter);
  }

  function traverse(iter){
    return new Promise((res, rej) => {
    
      function step(err, arg) {
        let value, done;
        
        try {
          ({ value, done } = err ? iter.throw(err) : iter.next(arg)); 
        } catch(e){
          rej(e);
        }
  
        if (done) {
          res(value);
          return;
        }
        
        Promise.resolve(value).then(
          res => step(null, res),
          rej => step(rej));
      } 
    
      step();
    });
  }
}