Add support for promises with Node Sync.

sync-promise.js

// Add support for promises with Node Sync.
// https://github.com/ybogdanov/node-sync
(function() {
  'use strict';
  const { Fibers, Future } = module.exports = require('sync');
  const slice = Function.prototype.call.bind(Array.prototype.slice);

  if(typeof Promise !== 'undefined') {
    // Pause execution and wait until the promise fufilled.
    Promise.prototype.sync = function() {
      const fiber = Fibers.current;
      let err, result, yielded, called;
      this.then(function(value) {
        if(called) return;
        called = true;
        result = arguments.length > 1 ?
          slice(arguments) : value;
        if(yielded) fiber.run();
      }, function(reason) {
        if(called) return;
        called = true;
        err = reason;
        if(yielded) fiber.run();
      });
      if(!called) {
        yielded = true;
        Fibers.yield();
      }
      if(err) throw err;
      return result;
    };
    
    // Converts a promise to future.
    Promise.prototype.toFuture = function() {
      const future = new Future();
      this.then(function() {
        const args = slice(arguments);
        args.unshift(null);
        future.apply(null, args);
      }, future);
      return future;
    };
  }
})();