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# run-queue A promise based, dynamic priority queue runner, with concurrency limiting. ```js const RunQueue = require('run-queue') const queue = new RunQueue({ maxConcurrency: 1 }) queue.add(1, example, [-1]) for (let ii = 0; ii < 5; ++ii) { queue.add(0, example, [ii]) } const finished = [] queue.run().then( console.log(finished) }) function example (num, next) { setTimeout(() => { finished.push(num) next() }, 5 - Math.abs(num)) } ``` would output ``` [ 0, 1, 2, 3, 4, -1 ] ``` If you bump concurrency to `2`, then you get: ``` [ 1, 0, 3, 2, 4, -1 ] ``` The concurrency means that they don't finish in order, because some take longer than others. Each priority level must finish entirely before the next priority level is run. See [PRIORITIES](https://github.com/iarna/run-queue#priorities) below. This is even true if concurrency is set high enough that all of the regular queue can execute at once, for instance, with `maxConcurrency: 10`: ``` [ 4, 3, 2, 1, 0, -1 ] ``` ## API ### const queue = new RunQueue(options) Create a new queue. Options may contain: * maxConcurrency - (Default: `1`) The maximum number of jobs to execute at once. * Promise - (Default: global.Promise) The promise implementation to use. ### queue.add (prio, fn, args) Add a new job to the end of the queue at priority `prio` that will run `fn` with `args`. If `fn` is async then it should return a Promise. ### queue.run () Start running the job queue. Returns a Promise that resolves when either all the jobs are complete or a job ends in error (throws or returns a rejected promise). If a job ended in error then this Promise will be rejected with that error and no further queue running will be done. ## PRIORITIES Priorities are any integer value >= 0. Lowest is executed first. Priorities essentially represent distinct job queues. All jobs in a queue must complete before the next highest priority job queue is executed. This means that if you have two queues, `0` and `1` then ALL jobs in `0` must complete before ANY execute in `1`. If you add new `0` level jobs while `1` level jobs are running then it will switch back processing the `0` queue and won't execute any more `1` jobs till all of the new `0` jobs complete.