batchasync.js/README.md

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# [batchasync.js](https://git.coolaj86.com/coolaj86/batchasync.js)
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Like calling `map()` and resolving with `Promise.all()`,
but handling a bounded number of items at any given time.
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Want to read about it?
- [Batching async requests in < 50 lines of VanillaJS](https://coolaj86.com/articles/batching-async-requests-50-lines-of-vanilla-js/)
# Install
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```bash
npm install --save batchasync
```
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# Usage
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```js
// Browsers
var batchAsync = window.batchAsync;
```
```js
// Node
var batchAsync = require('batchasync').batchAsync;
```
```js
var batchSize = 4;
var things = ['apples', 'bananas', 'pears'];
function doStuff() {
// ... go fetch things
}
batchAsync(batchSize, things, doStuff).then(function(results) {
// all results, in order, just like Promise.all()
console.log(results[0]);
});
```
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## A note on `undefined`
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Returning `undefined` will cause an exception to be thrown,
and the Promise to be rejected.
This is on purpose - because `undefined` is indistinguishable from a skipped Promise.
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Return `null` instead.
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**Example (bad)**:
```js
function doStuff(thing) {
// Oops! forgot to return
request('https://searchallthe.pictures/api/' + thing);
}
```
**Example (good)**:
```js
function doStuff(thing) {
return request('https://searchallthe.pictures/api/' + thing);
}
```
**Example (good)**:
```js
function doStuff(thing) {
return null;
}
```