我想使用promise,但我有一个回调API,格式如下:
1.DOM加载或其他一次性事件:
window.onload; // set to callback
...
window.onload = function() {
};
2.普通回调:
function request(onChangeHandler) {
...
}
request(function() {
// change happened
...
});
3.节点样式回调(“nodeback”):
function getStuff(dat, callback) {
...
}
getStuff("dataParam", function(err, data) {
...
})
4.具有节点样式回调的整个库:
API;
API.one(function(err, data) {
API.two(function(err, data2) {
API.three(function(err, data3) {
...
});
});
});
我如何在promise中使用API,如何“promise”它?
也许已经回答了,但我通常是这样做的:
// given you've defined this `Future` fn somewhere:
const Future = fn => {return new Promise((r,t) => fn(r,t))}
// define an eventFn that takes a promise `resolver`
const eventFn = resolve => {
// do event related closure actions here. When finally done, call `resolve()`
something.oneventfired = e => {resolve(e)}
}
// invoke eventFn in an `async` workflowFn using `Future`
// to obtain a `promise` wrapper
const workflowFn = async () => {await Future(eventFn)}
特别是对于indexedDb事件包装器之类的东西,以简化使用。
或者你可能会发现未来的这种变化更具普遍性
class PromiseEx extends Promise {
resolve(v,...a) {
this.settled = true; this.settledValue = v;
return(this.resolve_(v,...a))
}
reject(v,...a) {
this.settled = false; this.settledValue = v;
return(this.reject_(v,...a))
}
static Future(fn,...args) {
let r,t,ft = new PromiseEx((r_,t_) => {r=r_;t=t_})
ft.resolve_ = r; ft.reject_ = t; fn(ft,...args);
return(ft)
}
}
我通常使用的一个简单的泛型函数。
const promisify = (fn, ...args) => {
return new Promise((resolve, reject) => {
fn(...args, (err, data) => {
if (err) {
return reject(err);
}
resolve(data);
});
});
};
如何使用它
函数promify接受带有回调的函数:
const cb = (result) => `The result is ${result}`;
const sum = (a, b, cb) => {
const result = a + b;
cb(result); // passing args to the callback function
}
// using the util
promise = promisify(sum, 3, 1, cb);
promise.then(x => console.log(x)) // 4
您可能不需要这个答案,但这将有助于了解可用实用程序的内部工作原理