（六十三）ES6新特征 - Async
1：基本概念
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封装了自动化执行并返回一个Promise的Generator函数语法糖封装了自动化执行脚本返回PromiseGenerator函数语法糖
function resolveAfter2Seconds(value) { return new Promise(resolve => { setTimeout(() => { resolve(value); }, 2000); }); }; const generator = function* () { const value1 = yield resolveAfter2Seconds(1); const value2 = yield resolveAfter2Seconds(2); console.log(value1); console.log(value2); }; function co(generatorFunction) { return new Promise(function(resolve, reject) { const generator = generatorFunction(); 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 generator.next(v); }); }, function(e) { step(function() { return generator.throw(e); }); }); } step(function() { return generator.next(undefined); }); }); } co(generator); /* (4s后) 1 2 */ const async = async function () { const value1 = await resolveAfter2Seconds(1); const value2 = await resolveAfter2Seconds(2); console.log(value1); console.log(value2); }; async().then(res => { console.log(res); }) /* (4s后) 1 2 */ async function asyncFunc() {}; const asyncFunc = async function () {}; const asyncFunc = async () => {}; const obj = { async asyncFunc() {} }
