51 lines
2.1 KiB
Markdown
51 lines
2.1 KiB
Markdown
---
|
|
title: debouncePromise
|
|
tags: function,promise,advanced
|
|
firstSeen: 2020-10-10T21:09:04+03:00
|
|
lastUpdated: 2020-10-19T18:51:03+03:00
|
|
---
|
|
|
|
Creates a debounced function that returns a promise, but delays invoking the provided function until at least `ms` milliseconds have elapsed since the last time it was invoked.
|
|
All promises returned during this time will return the same data.
|
|
|
|
- Each time the debounced function is invoked, clear the current pending timeout with `clearTimeout()` and use `setTimeout()` to create a new timeout that delays invoking the function until at least `ms` milliseconds has elapsed.
|
|
- Use `Function.prototype.apply()` to apply the `this` context to the function and provide the necessary arguments.
|
|
- Create a new `Promise` and add its `resolve` and `reject` callbacks to the `pending` promises stack.
|
|
- When `setTimeout` is called, copy the current stack (as it can change between the provided function call and its resolution), clear it and call the provided function.
|
|
- When the provided function resolves/rejects, resolve/reject all promises in the stack (copied when the function was called) with the returned data.
|
|
- Omit the second argument, `ms`, to set the timeout at a default of `0` ms.
|
|
|
|
```js
|
|
const debouncePromise = (fn, ms = 0) => {
|
|
let timeoutId;
|
|
const pending = [];
|
|
return (...args) =>
|
|
new Promise((res, rej) => {
|
|
clearTimeout(timeoutId);
|
|
timeoutId = setTimeout(() => {
|
|
const currentPending = [...pending];
|
|
pending.length = 0;
|
|
Promise.resolve(fn.apply(this, args)).then(
|
|
data => {
|
|
currentPending.forEach(({ resolve }) => resolve(data));
|
|
},
|
|
error => {
|
|
currentPending.forEach(({ reject }) => reject(error));
|
|
}
|
|
);
|
|
}, ms);
|
|
pending.push({ resolve: res, reject: rej });
|
|
});
|
|
};
|
|
```
|
|
|
|
```js
|
|
const fn = arg => new Promise(resolve => {
|
|
setTimeout(resolve, 1000, ['resolved', arg]);
|
|
});
|
|
const debounced = debouncePromise(fn, 200);
|
|
debounced('foo').then(console.log);
|
|
debounced('bar').then(console.log);
|
|
// Will log ['resolved', 'bar'] both times
|
|
```
|