JS為什么說async/await是generator的語法糖詳解

function sleep(time) {
 return new Promise((resolve, reject) => {
 setTimeout(() => {
 resolve(1);
 }, time);
 });
}

async function test () {
 for(let i = 0; i < 10; i++) {
 let result = await sleep(1000);
 console.log(result);
 }
}

let test = function () {
 // ret 為一個Promise對象，因為ES6語法規(guī)定 async 函數(shù)的返回值必須是一個 promise 對象
 let ret = _asyncToGenerator(function* () {
 for (let i = 0; i < 10; i++) {
 let result = yield sleep(1000);
 console.log(result);
 }
 });
 return ret;
}();

// generator 自執(zhí)行器
function _asyncToGenerator(genFn) {
 return new Promise((resolve, reject) => {
 let gen = genFn();
 function step(key, arg) {
 let info = {};
 try {
 info = gen[key](arg);
 } catch (error) {
 reject(error);
 return;
 }
 if (info.done) {
 resolve(info.value);
 } else {
 return Promise.resolve(info.value).then((v) => {
 return step('next', v);
 }, (error) => {
 return step('throw', error);
 });
 }
 }
 step('next');
 });
}