SOURCE

// Generator函数的自动执行器

// 简易版写法
function spawn(genF) {
    return new Promise(function(resolve, reject) {
        const gen = genF();
        function step(data) {
            const next = gen.next(data);

            if (next.done) return resolve(next.value);

            Promise.resolve(next.value).then(step).catch(reject);
        };
        step();
    });
};

// 复杂版，考虑错误捕获
function spawnEx(genF) {
    return new Promise(function(resolve, reject) {
        const gen = genF();
        function step(nextF) {
            let next;
            try {
                next = nextF();
            } catch (e) {
                return reject(e);
            };

            if (next.done) {
                return resolve(next.value);
            };

            Promise.resolve(next.value).then(function(v) {
                step(function() { return gen.next(v); });
            }, function(e) {
                step(function() { return gen.throw(e); });
            });
        };
        step(function() { return gen.next(undefined); });
    });
}

async function wait(ms) {
    return new Promise((res, rej) => {
        setTimeout(() => {
            res(new Date().valueOf());
        }, ms);
    });
}



spawnEx(function* () {
    var a = yield wait(1000);
    var b = yield wait(2000);
    return `第一种：${b-a}ms`;
}).then(v => {
    console.log(v);
}).catch(e => {
    console.log(e);
});

spawnEx(function* () {
    var a = wait(1000);
    var b = wait(1000);
    var c = yield a;
    var d = yield b;
    return `第二种：${d-c}ms`;
}).then(v => {
    console.log(v);
}).catch(e => {
    console.log(e);
});

// const gen = testGen();
// console.log(JSON.stringify(gen.next(undefined)));
// console.log(JSON.stringify(gen.next(123)));
// console.log(JSON.stringify(gen.next(100)));