[英]Javascript - Using generators instead of promises
suppose I have following functions: 假设我具有以下功能:
var f1 = function() {
console.log('running f1');
return new Promise(function(res, rej) {
setTimeout(() => res('resolved_1!'), 1000);
});
};
var f2 = function(a) {
console.log('running f2 with ' + a);
return new Promise(function(res, rej) {
setTimeout(() => res('resolved_2!'), 2000);
});
};
var f3 = function() {
console.log('running f3');
return new Promise(function(res, rej) {
setTimeout(() => res('resolved_3!'), 3000);
});
};
I can run them with: 我可以使用以下命令运行它们:
let t1 = +new Date;
Promise.all([
f1().then(a => {
return f2(a);
}),
f3()
]).then((result) => {
let t2 = +new Date;
console.log(t2 - t1);
});
And it takes roughly 3 seconds. 大约需要3秒钟。
Now I want to run these functions using generators: 现在,我想使用生成器运行以下功能:
let t1 = +new Date;
let result = yield [f1(), f3()];
yield f2(result[0]);
let t2 = +new Date;
console.log(t2 - t1)
Since I need resolved value of f1 to call f2 I shall wait for f1 to complete. 由于我需要解析的f1值才能调用f2,因此我将等待f1完成。 This takes 5 seconds.
这需要5秒钟。 How can I get the same 3 seconds but using generators?
如何使用发电机使用相同的3秒时间?
This takes 5 seconds.
这需要5秒钟。
See Slowdown due to non-parallel awaiting of promises in async generators . 请参阅减速,因为异步生成器中没有并行等待诺言 。
How can I get the same 3 seconds but using generators?
如何使用发电机使用相同的3秒时间?
You just have to express the same control flow: 您只需要表达相同的控制流程:
let t1 = +new Date;
let result = yield [f1().then(f2), f3()];
let t2 = +new Date;
console.log(t2 - t1)
If you want to avoid then
for some reason, and use generators instead, it would have to be 如果你想避免
then
出于某种原因,并使用发电机,相反,它必须是
let t1 = +new Date;
let result = yield [co(function*() {
var a = yield f1();
return yield f2(a); // yield is optional here
}), f3()];
let t2 = +new Date;
console.log(t2 - t1)
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