# throat Throttle the parallelism of an asynchronous, promise returning, function / functions. This has special utility when you set the concurrency to `1`. That way you get a mutually exclusive lock. [](https://travis-ci.org/ForbesLindesay/throat) [](https://coveralls.io/r/ForbesLindesay/throat?branch=master) [](https://david-dm.org/ForbesLindesay/throat) [](https://www.npmjs.com/package/throat) [](https://greenkeeper.io/) [](https://saucelabs.com/u/throat) ## Installation npm install throat ## API ### throat(concurrency) This returns a function that acts a bit like a lock (exactly as a lock if concurrency is 1). Example, only 2 of the following functions will execute at any one time: ```js const throat = require('throat')(2); // alternatively provide your own promise implementation const throat = require('throat')(require('promise'))(2); const promise = Promise.resolve(); const resA = throat(() => /* async stuff... */ promise); const resB = throat(() => /* async stuff... */ promise); const resC = throat(() => /* async stuff... */ promise); const resD = throat(() => /* async stuff... */ promise); const resE = throat(() => /* async stuff... */ promise); ``` ### throat(concurrency, worker) This returns a function that is an exact copy of `worker` except that it will only execute up to `concurrency` times in parallel before further requests are queued: ```js const throat = require('throat'); // alternatively provide your own promise implementation const throat = require('throat')(require('promise')); const input = ['fileA.txt', 'fileB.txt', 'fileC.txt', 'fileD.txt']; const data = Promise.all(input.map(throat(2, fileName => readFile(fileName)))); ``` Only 2 files will be read at a time, sometimes limiting parallelism in this way can improve scalability. ## License MIT