No matter how frequently you request a resource, only make one request at a time
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readme.md

The gate-keeper!

If you have some remote resource you want to fetch, and you could be requesting a bunch of times, you probably don't need more than one request going at a time.

This library uses Promises. For the callback version, see the 1.x branch.

Pairs very well with the key-master.

Install

npm install gate-keeper

const gateKeeper = require('gate-keeper')

Example

let calledAlready = false
const get = gateKeeper(function getSomeRemoteResource({ isCancelled }) {
	// this function will only be called once, and in this example
	// won't be called again afterward.
	calledAlready // => false
	
	calledAlready = true
	
	return new Promise(resolve => {
		setTimeout(function() {
			isCancelled() // => false
			resolve('A successful value')
		}, 50)
	})
})

get().then(value => {
	// err => null
	// value => 'A successful value'
})
get().then(value => {
	// value => 'A successful value'
	get.isCurrentlyGetting() // => false
})

get.isCurrentlyGetting() // => true

API

const get = gateKeeper(asyncGetterFunction)

Returns a get function that you can use whenever you want to trigger calling asyncGetterFunction.

asyncGetterFunction should return a promise. Until that promise is resolved or rejected, asyncGetterFunction will not be called again.

Your asyncGetterFunction function will be passed an object with a property named isCancelled, a function you can call that returns true or false depending on whether or not the gatekeeper's cancel method was called while the request was running.

get()

Triggers the asyncGetterFunction if it is not running already. Returns the promise associated with the currently-running getter.

get.isCurrentlyGetting()

Returns true if the asyncGetterFunction is in progress, false otherwise.

get.cancel()

If the asyncGetterFunction is in progress, its results are ignored. Promises that are unresolved when cancel is called will never resolve.

Using with the key-master

Because you probably have more than one remote resource you could be fetching.

const keyMaster = require('key-master')

const fetchers = keyMaster(key => gateKeeper(() => Promise.resolve(key + ' is awesome!')))

fetchers.get('pie')(value => {
	value // => 'pie is awesome!'
})
fetchers.get('cake')(value => {
	value // => 'cake is awesome!'
})
fetchers.get('pie')(value => {
	value // => 'pie is awesome!'
})

License

WTFPL