promise limit loop

npm i promise-limit-loop

this package support loop with promise, you dont need to create an array of pending promise before executing

PromiseLimitLoop.map(array, limit, iterator)

this method loop all values in array, send them to iterator (params of iterator like array.map)

• array: an array like [1,2,3,4]
• limit: limit promise executed at same time
• iterator: receive and process value

PromiseLimitLoop.forEach(array, limit, iterator)

like PromiseLimitLoop.map but doesn't return result

PromiseLimitLoop.for(from, to, limit, iterator, step = 1)

• from: number
• to: number
• step: number

loop from 'from' to 'to', value will be sent to iterator

If step > 0, from must less than to

If step < 0, from must greater than to

PromiseLimitLoop.while(conditionFunc, generatorFunc, limit, iterator, [generatorParams])

• conditionFunc(*): while conditionFunction return truly, the loop will continue executing
• generatorFunc: each loop round, iterator will receive value return from this function
• generatorParams: will pass to generator each loop

~~PromiseLimitLoop.until~~ use PromiseLimitLoop.doWhile

PromiseLimitLoop.doWhile(conditionFunc, generatorFunc, limit, iterator, [generatorParams])

• conditionFunc(*): execute the loop, until the conditionFunc return falsy
• generatorFunc: each loop round, iterator will receive value return from this function
• generatorParams: will pass to generator each loop

conditionFunc(*): pushing generatorFunc to Queue will execute conditionFunc to validate.

PromiseLimitLoop.doWhile: execute after pushing

PromiseLimitLoop.while: execute before pushing

PromiseLimitLoop.parallel((handleLimit: (increaseOrDecrease?: number, directlySetToLimit?: boolean)=> number))

• handleLimit: increase or decrease limit of promise executing. If pass non or null params, return current limit. To set limit directly, pass second param as true

PromiseLimitLoop.parallel(10, async (handleLimit) => {
  handleLimit(0, true) // set limit to 0 to force stop
})

• executionTime: the current total time of executing promise
• Call handleLimit(-1) will decrease limit by 1, and increase limit by 1 if call handleLimit(1)
• If the limit is 0 or negative, the promise will be executed immediately

example

const PromiseLimitLoop = require('promise-limit-loop')
const start = Date.now()
PromiseLimitLoop.for(0, 10, 2, async function (i) {
  return new Promise(resolve => {
    setTimeout(() => {
      console.log(i, Date.now() - start)
      resolve()
    }, 1e3)
  })
})
/**
0 1003
1 1010
2 2013
3 2013
4 3014
5 3014
6 4014
7 4015
8 5019
9 5020
10 6025
*/

// map is same
PromiseLimitLoop.forEach(['a', 'b', 'c', 'd', 'e', 'f'], 2, async function (i) {
  return new Promise(resolve => {
    setTimeout(() => {
      console.log(i, Date.now() - start)
      resolve()
    }, 1e3)
  })
})
/**
a 1004
b 1011
c 2015
d 2015
e 3020
f 3020
*/

let i = 0
PromiseLimitLoop.doWhile(
  async function condition () {
    return new Promise(resolve => setTimeout(() => {
      resolve(Date.now() - start < 3e3) // stop if 3 sec passed
    }, 1e3)) // delay 1sec before each loop
  },
  async function generator () {
    return i++
  },
  3,
  async function (i) {
    console.log(i, Date.now() - start)
  }
)
.then(() => {
  console.log('done', Date.now() - start)
})
/**
0 0
1 5
2 5
3 1007
4 1007
5 1007
6 2010
7 2010
8 2010
done 3010 // exit when time > 3s
*/