pending-queue ensures a certain asynchronous method only run once, and queues listeners which are registered to it.

$ npm install pending-queue --save

const Queue = require('pending-queue')

let counter = 0
const queue = new Queue({
  load: (a, b) => {
    return new Promise((resolve) => {
      counter ++
      setTimeout(() => {
        resolve(a + b)
      }, 100)
    })
  }
})

function run () {
  queue.add(1, 2).then((value) => {
    console.log(value, counter)
  })
}

run()
run()
run()

// 3, 1
// 3, 1
// 3, 1

// So the load function ran only once.

• load function(...params) the method to get the value
• stringify function(params)=JSON.stringify stringify the parameters as the key to queue all asynchronous requests.

Returns EventEmitter, and key as the event name, so you can use queue.listenerCount(key) to see if there are pending tasks.

• load

• params Arguments which will be passed into load

Returns Promise

• key String

Return Promise

Specifies the key ourself, and avoid using options.stringify to serialize the key from params.

But pay attension that there should be a consistent one-to-one match between key and params, or make sure that you exactly know what you are doing.

MIT