实现一个简单的promise

1、最基本的功能：

function Promise(fn){this.arr = [];
    this.then = function(thParam){thParam(this.arr);
        //return this;
    };
    var that = this;
    function resolve(parm){that.arr.push(parm);
        console.log(parm)
    }
    fn(resolve);
}

var p1 = new Promise(function(resolve){resolve("参数给 then");
});
p1.then(function(response){console.log(response)
});

2、链式调用
加上一个 return this 就可以了

function Promise(fn){this.arr = [];
    this.then = function(thParam){thParam(this.arr);
        return this;
    };
    var that = this;
    function resolve(parm){that.arr.push(parm);
        console.log(parm)
    }
    fn(resolve);
}

var p1 = new Promise(function(resolve){resolve("参数给 then");
});
p1.then(function(response){console.log(response)
}).then(function(response){console.log(response)
});

参考资料：手写一个 Promise