Function throttling and function stabilization in JS (detailed tutorial)

This article mainly introduces the analysis of JS function throttling and function anti-shake problems. It is very good and has reference value. Friends in need can refer to it

Question 1: If the dom drag and drop function is implemented , but when binding the drag event, I found that every time the element moved a little bit, a large number of callback functions were triggered, causing the browser to freeze directly. What should I do at this time?

**Question 2: **If a button is bound to the post event of form submission, but the user sometimes clicks multiple times under extremely poor network conditions The button causes the form to be submitted repeatedly. How to prevent multiple submissions?

In order to deal with the above scenario, the two concepts of function anti-shake and function throttling have emerged. In general:

These two methods are to control the number of executions of the function on the timeline. .

Function debounce(debounce)

Concept: Execute the callback n seconds after the event is triggered. If the event is triggered again within n seconds, is triggered, the timer will restart.

Examples in life: If someone enters the elevator (triggers the event), the elevator will depart in 10 seconds (execute the event listener). At this time, if someone enters the elevator again (again within 10 seconds) trigger the event), we have to wait another 10 seconds before starting (re-timing).

Function throttling (throttle)

Concept: Specifies a unit time. Within this unit time, there can only be one trigger event. The callback function is executed. If an event is triggered multiple times in the same unit of time, only one event will take effect.

Examples in life: We know that a current saying is that when more than 24 pictures are played continuously within 1 second, a coherent animation will be formed in the human vision, so in the movie The playback (used to be, but I don’t know now) is basically played at a speed of 24 pictures per second. Why not 100 pictures or more? Because when 24 pictures can meet the needs of human vision, 100 pictures will seem to be a waste of resources. .

Analysis Chart

Assume that the total time of our observation is 10 seconds, and 1 second is specified as the minimum interval time for an event.

If the frequency of trigger events is 0.5s/time, then the function anti-shake is as shown in the figure

Because it is never possible to wait for one second before being triggered again , so in the end none of the events was successful.

Function throttling is shown in the figure

Because it is controlled at most once per second, the frequency is 0.5s/time, so there is one event every second void. The final control is 1s/time

If the frequency of triggering events is 2s/time, then the

function anti-shake is as shown

because 2s/time
is already greater than the specified minimum time, so it is triggered every two seconds.

The function throttling is as shown in the figure

Similarly, 2s/time is greater than the minimum time requirement, so every trigger takes effect.

Application scenarios

For function anti-shake, there are the following application scenarios:

• Add function anti-shake to the button to prevent the form from being submitted multiple times.

• When performing AJAX verification for continuous input in the input box, using function anti-shake can effectively reduce the number of requests.

• Determine whether the scroll slides to the bottom and anti-shake the scroll event function

In general, it is suitable for responding to multiple events at one time

For function throttling, there are the following scenarios:

• Refresh rate in the game

• DOM element drag

• Canvas brush function

In general, it is suitable for a large number of events to be evenly distributed and triggered according to time.

Source code

Function anti-shake:

function debounce(fn, wait) {
 var timer = null;
 return function () {
  var context = this
  var args = arguments
  if (timer) {
   clearTimeout(timer);
   timer = null;
  }
  timer = setTimeout(function () {
   fn.apply(context, args)
  }, wait)
 }
}
var fn = function () {
 console.log('boom')
}
setInterval(debounce(fn,500),1000) // 第一次在1500ms后触发，之后每1000ms触发一次
setInterval(debounce(fn,2000),1000) // 不会触发一次（我把函数防抖看出技能读条，如果读条没完成就用技能，便会失败而且重新读条）

The reason why it returns a function is because the anti-shake itself is more like a Function modification, so I did a function currying. Closure is also used, and the variable of the closure is timer.

Function throttling

function throttle(fn, gapTime) {
 let _lastTime = null;
 return function () {
 let _nowTime = + new Date()
 if (_nowTime - _lastTime > gapTime || !_lastTime) {
  fn();
  _lastTime = _nowTime
 }
 }
}
let fn = ()=>{
 console.log('boom')
}
setInterval(throttle(fn,1000),10)

The picture shows a simple function throttling implemented, the result is a boom once a second

The above is what I compiled for everyone. I hope it will be helpful to everyone in the future.

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