verify this condition prior to executing the for loop in javascript

When working with a queue in Typescript (ES6) set to run on an interval of 1 ms, it's important to consider the most efficient approach for performance.

1.

setInterval(() => {
  //if (this._queue.filter(a => !a.running && a.cbs.length) { // incorrect
  if (this._queue.filter(a => !a.running && a.cbs.length).length) { //edit
    for (let i = 0; i < this._queue.filter(a => !a.running && a.cbs.length).length; i++) {
      ...
    }
  }
}, 1);
setInterval(() => {
  for (let i = 0; i < this._queue.filter(a => !a.running && a.cbs.length).length; i++) {
    ...
  }
}, 1);

Approach #1 includes an additional line of code but may require less CPU computation during each iteration of the interval. Is this assumption accurate?

On the other hand, Approach #2 involves defining 'i', filtering the queue, and then iterating through it.

The difference in performance between the two approaches may be minimal, but I am curious to understand the potential impact nonetheless.

Answer №1

Your if statement needs correction

if (this._queue.filter(a => !a.running && a.cbs.length) {
// this always resolves as true
// should be
if (this._queue.filter(a => !a.running && a.cbs.length).length) {

You can optimize by reusing the iteration process

setInterval(() => {
  const arr = this._queue.filter(a => !a.running && a.cbs.length)
  if (arr.length) {
    for (let i = 0; i < arr.length; i++) {
      ...
    }
  }
}, 1);

Answer №2

When handling both cases, it's important to optimize the evaluation of the filter expression by only doing it once:

setInterval(() => {
  const numTasks = this._queue.filter(task => !task.running && task.callbacks.length).length;
  for (let j = 0; j < numTasks;  j++) {
    ...
  }
}, 1);

Answer №3

Take note to ensure that you assess the value of the filter beyond the for loop: Otherwise, you will be evaluating the filter's value with every iteration, even if it does not rely on the iteration:

You can confirm this by inserting a console log within the filter iterator.

setInterval(() => {
 for (let i = 0; i < const filteredQueue = this._queue.filter(a => !a.running && 
 a.cbs.length).length; i++) 
 {
 ...
 }
 }, 1);

Therefore, it is preferable to declare a constant with the value

this._queue.filter(a => !a.running && a.cbs.length)
outside of the loop

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