24 # co 库的实现

const fs = require("fs").promises;
// 代码更像是同步的，但是执行还是异步的
function* read() {
    let name = yield fs.readFile("./file/name.txt", "utf-8");
    let age = yield fs.readFile("./file/age.txt", "utf-8");
    return { name, age };
}
// 下面是需要优化的代码
let it = read();
let { value, done } = it.next();
value.then((data1) => {
    console.log("name---->", data1);
    let { value, done } = it.next(data1);
    value.then((data2) => {
        let { value, done } = it.next(data2);
        console.log("age---->", data2);
        console.log("return---->", value);
        // 还可以抛出异常
        // it.throw("泰裤辣");
    });
});

const co = (it) => {
    return new Promise((resolve, reject) => {
        // 异步迭代靠的是回调函数
        function next(data) {
            let { value, done } = it.next(data);
            if (!done) {
                // value 可能不是promise，需要包装一下
                Promise.resolve(value).then(next, reject);
            } else {
                resolve(value);
            }
        }
        // 先调用一次
        next();
    });
};
co(read()).then((data) => {
    console.log("data---->", data);
});