promise实现原理
伪代码
class my_promise {
constructor(fun) {
const that = this;
this._queue = []; // 队列
that._success_res = null;
that._error_res = null;
that.status = "";// 状态机
fun(
(...args) => {
that._success_res = args;
that.status = "success";
that._queue.forEach(json => {
json.fun1(...args);
});
},
(...args) => {
that._error_res = args;
that.status = "error";
that._queue.forEach(json => {
json.fun2(...args);
});
}
);
}
then(fun1, fun2) {
if (this.status === "success") {
fun1(this._success_res);
} else if (this.status === "error") {
fun2(this._error_res);
} else {
// 异步操作还没完
this._queue.push({ fun1, fun2 });
}
}
}
my_promise.all = arr => {
let list = [];
return new my_promise((resolve, reject) => {
let i = 0;
next();
function next() {
arr[i].then(res => {
list.push(res);
i++;
if (i === arr.length) {
resolve(list);
} else {
next();
}
}, reject);
}
});
};
