下面实现了一个控制流包装器,它使异步代码只能由yield关键字描述.
这基本上是什么时候async / await在ESwhatever中引起了什么?
co(function*() {
console.log('...');
yield one();
console.log('...');
yield two();
})
function co(gFn) {
var g = gFn();
return Promise.resolve()
.then(go);
function go() {
var result = g.next();
if(result.done) {
return;
}
if(isPromise(result.value)) {
return result.value.then(go); // Promises block until resolution.
}
return Promise.resolve(result);
}
}
function isPromise(o) {
return o instanceof Promise;
}
function one() {
return new Promise(resolve => setTimeout(() => (console.log('one'), resolve()), 1000));
}
function two() {
return new Promise(resolve => setTimeout(() => (console.log('two'), resolve()), 1000));
}
编辑:
根据我更新的回复,考虑到返回值:
co(function*() {
console.log('...');
const result1 = yield one();
console.log('result1: ', result1);
const result2 = yield two();
console.log('result2: ', result2);
const result3 = yield[one(), two()];
console.log('result3: ', result3);
const result4 = yield{
one: one(),
two: two()
};
console.log('result4: ', result4);
})
function co(gFn) {
var g = gFn();
return Promise.resolve().then(go);
function go() {
var result = g.next(...arguments);
if (isPromise(result.value)) {
return result.value.then(go);
}
if (Array.isArray(result.value)) {
return Promise.all(result.value).then(go);
}
if (isObject(result.value)) {
var o = {};
var promises = Object.keys(result.value).map(k=>result.value[k].then(r=>o[k] = r));
return Promise.all(promises).then(()=>o).then(go);
}
return Promise.resolve(result);
}
}
function isPromise(o) {
return o instanceof Promise;
}
function isObject(val) {
return val && (Object === val.constructor);
}
function one() {
return new Promise(resolve=>setTimeout(()=>(console.log('one'),
resolve('result 1')), 1000));
}
function two() {
return new Promise(resolve=>setTimeout(()=>(console.log('two'),
resolve('result 2')), 1000));
}
解决方法:
Is this basically what async/await does under the hood in ESwhatever?
并不是的.对于做同样的事情,这是一种不同的方法.什么异步/等待变成更像
async function foo() {
const bar = await Bar();
bar ;
const baz = await Baz(bar);
return baz;
}
变
function foo() {
return Bar()
.then(bar => {
bar ;
return Baz(bar)
.then(baz => {
return baz;
});
});
}
来源:https://www./content-1-469401.html
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