Generator & yield write in sync way

Generator & yield write in sync way

var p = new Promise(function(resolve, reject){
  setTimeout(function(){
    console.log(2);
    resolve(2);
  },1000);
});

var p2 = new Promise(function(resolve, reject){
  setTimeout(function(){
    console.log(3);
    resolve(3);
  },1500);
});

function runGenerator(g) {
    var it = g(), ret;
    (function iterate(val){
        // console.log(val);
        ret = it.next( val );  //generator对象next()的值  就是 yield 语句后面表达式的值
        if (!ret.done) {
            // 检查是否已经then完成
            if ("then" in ret.value) {  //当yield后的表达式是 promise对象的时候
                // 这一句很关键
                ret.value.then( iterate );
                //记得promise的then如何调用的吗 p.then(function(data){...}) 这样resolve的值就传到iterator中了
            }
            else {
                // 同步回调的trick
                setTimeout( function(){
                    iterate( ret.value );
                }, 0 );
            }
        }
    })();
}

runGenerator(function* (){
    var result = yield p;
    console.log(1, result);
    var result = yield p2;
    console.log(result);
})