nodejs的co简单实现

function co(gen) {
  var g = gen();
  var next = g.next();
  var res = next.value;
  function _next(next, res) {
    if (!next.done) {
      if (res && res.constructor == Promise) {
        res.then(function (val) {
          next = g.next(val);
          res = next.value;
          _next(next, res);
        });
      } else if (res.constructor == Function) {
        var fn = res;
        fn(function (err, res) {
          next = g.next(res);
          res = next.value;
          _next(next, res);
        });
      } else {
        next = g.next(res);
        res = next.value;
        _next(next, res);
      }
    }
  }
  _next(next, res);
}

var fs = require("fs");
var readThunk = thunkify(fs.readFile);
 
 
co(function * gen() {
    var pro = new Promise(function(resolve, reject) {
        resolve(1999);
    });
    var r3=  yield pro;
    var r1 = yield 100;
    var r2 = yield 200;
    var a = yield readThunk("./a.html");
    var c = yield function (fn) {
        setTimeout(function() {
            fn(null, 188);
        }, 1000)
    }
    console.log(r3, r1, r2, a);
    console.log(c);
})
 
 
// 结果
1999 100 200
188