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對象next()的值  就是 yield 語句後面表達式的值  
        if (!ret.done) {
            // 檢查是否已經then完成
            if ("then" in ret.value) {  //當yield後的表達式是 promise對象的時候
                // 這一句很關鍵
                ret.value.then( iterate );  
                //記得promise的then如何調用的嗎 p.then(function(data){...}) 這樣resolve的值就傳到iterator中了
            }
            else {
                // 同步回調的trick
                setTimeout( function(){
                    iterate( ret.value );
                }, 0 );
            }
        }
    })();
}



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