本文的示例代碼參考co

目錄

• Generator

• co

• Source-Code

Generator

function* foo() {
    yield console.log('1');
    yield console.log('2');
}

var g = foo();
g.next(); // 1
g.next(); // 2

更多關(guān)于Generator函數(shù)可以參考Generator 函數(shù)的語法

co

cnpm i --save co

var co = require('co');

function* foo() {
    yield Promise.resolve(console.log('1'));
    yield Promise.resolve(console.log('2'));
}

co(foo); // 1 2

co適用于: Generator函數(shù)的yield命令后面 只能是Thunk函數(shù)或Promises對象

Source Code

• co實現(xiàn)的核心代碼只有以下的區(qū)區(qū)40行

function co(gen) {
    var ctx = this;
    var args = slice.call(arguments, 1);

    return new Promise(function (resolve, reject) {
        if (typeof gen === 'function') gen = gen.apply(ctx, args);
        if (!gen || typeof gen.next !== 'function') return resolve(gen);

        onFulfilled();

        function onFulfilled(res) {
            var ret;
            try {
                ret = gen.next(res);
            } catch (e) {
                return reject(e);
            }
            next(ret);
            return null;
        }

        function onRejected(err) {
            var ret;
            try {
                ret = gen.throw(err);
            } catch (e) {
                return reject(e);
            }
            next(ret);
        }

        function next(ret) {
            if (ret.done) return resolve(ret.value);
            var value = toPromise.call(ctx, ret.value);
            if (value && isPromise(value)) return value.then(onFulfilled, onRejected);
            return onRejected(new TypeError('You may only yield a function, promise, generator, array, or object, '
                + 'but the following object was passed: "' + String(ret.value) + '"'));
        }
    });
}

function toPromise(obj) {
    if (!obj) return obj;
    if (isPromise(obj)) return obj;
    if (isGeneratorFunction(obj) || isGenerator(obj)) return co.call(this, obj);
    if ('function' == typeof obj) return thunkToPromise.call(this, obj);
    if (Array.isArray(obj)) return arrayToPromise.call(this, obj);
    if (isObject(obj)) return objectToPromise.call(this, obj);
    return obj;
}

更多關(guān)于co的源碼可以參考co/index.js

• 完整的流程示意圖如下

co-logic-01.png

更多關(guān)于Promise可以參考Promise 對象

參考

• co.js - 讓異步代碼同步化

• co 函數(shù)庫的含義和用法

• 神奇的co