有人可以解释 Javascript 中的“去抖动”功能吗
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【中文标题】有人可以解释 Javascript 中的“去抖动”功能吗【英文标题】：Can someone explain the "debounce" function in Javascript 【发布时间】：2021-04-30 02:53:51 【问题描述】：我对javascript中的“去抖动”功能感兴趣，写在这里：http://davidwalsh.name/javascript-debounce-function
不幸的是，代码解释得不够清楚，我无法理解。谁能帮我弄清楚它是如何工作的（我在下面留下了我的 cmets）。总之我真的不明白这是怎么回事
// Returns a function, that, as long as it continues to be invoked, will not
// be triggered. The function will be called after it stops being called for
// N milliseconds.
function debounce(func, wait, immediate)
var timeout;
return function()
var context = this, args = arguments;
var later = function()
timeout = null;
if (!immediate) func.apply(context, args);
;
var callNow = immediate && !timeout;
clearTimeout(timeout);
timeout = setTimeout(later, wait);
if (callNow) func.apply(context, args);
;
;
编辑：复制的代码 sn-p 以前在错误的位置有 callNow。
【问题讨论】：
如果您调用clearTimeout 时使用的不是有效的计时器 ID，它不会执行任何操作。
@false，这是有效的标准行为吗？
@Pacerier 是的，它是in the spec：“如果句柄在调用该方法的WindowTimers 对象的活动计时器列表中没有标识条目，则该方法什么也不做。 "
这个博客很有帮助loopinfinito
【参考方案1】：
问题中的代码与链接中的代码略有不同。在链接中，在创建新的超时之前检查了(immediate && !timeout)。拥有它之后会导致立即模式永远不会触发。我已更新我的答案以从链接中注释工作版本。
function debounce(func, wait, immediate)
// 'private' variable for instance
// The returned function will be able to reference this due to closure.
// Each call to the returned function will share this common timer.
var timeout;
// Calling debounce returns a new anonymous function
return function()
// reference the context and args for the setTimeout function
var context = this,
args = arguments;
// Should the function be called now? If immediate is true
// and not already in a timeout then the answer is: Yes
var callNow = immediate && !timeout;
// This is the basic debounce behaviour where you can call this
// function several times, but it will only execute once
// [before or after imposing a delay].
// Each time the returned function is called, the timer starts over.
clearTimeout(timeout);
// Set the new timeout
timeout = setTimeout(function()
// Inside the timeout function, clear the timeout variable
// which will let the next execution run when in 'immediate' mode
timeout = null;
// Check if the function already ran with the immediate flag
if (!immediate)
// Call the original function with apply
// apply lets you define the 'this' object as well as the arguments
// (both captured before setTimeout)
func.apply(context, args);
, wait);
// Immediate mode and no wait timer? Execute the function..
if (callNow) func.apply(context, args);
/////////////////////////////////
// DEMO:
function onMouseMove(e)
console.clear();
console.log(e.x, e.y);
// Define the debounced function
var debouncedMouseMove = debounce(onMouseMove, 50);
// Call the debounced function on every mouse move
window.addEventListener('mousemove', debouncedMouseMove);【讨论】：
用于immediate && timeout 检查。不会总是有timeout （因为timeout 更早被调用）。另外，clearTimeout(timeout) 有什么好处，当它被声明（使其未定义）并被清除时，更早
immediate && !timeout 检查用于当使用immediate 标志配置去抖动时。这将立即执行该函数，但在 if 可以再次执行之前施加 wait 超时。所以!timeout 部分基本上是在说“对不起，小伙子，这已经在定义的窗口内执行了”...记住 setTimeout 函数将清除它，允许执行下一次调用。
为什么必须在setTimeout 函数中将超时设置为空？另外，我已经尝试过这段代码，对我来说，传入true for immediate 只会阻止函数被调用（而不是在延迟后被调用）。你会遇到这种情况吗？
我有一个关于立即的类似问题？为什么它需要立即参数。将 wait 设置为 0 应该具有相同的效果，对吧？正如@Startec 提到的，这种行为很奇怪。
如果您只是调用该函数，那么您不能在再次调用该函数之前强加一个等待计时器。想象一个用户捣碎开火键的游戏。您希望立即触发该火灾，但无论用户按下按钮的速度有多快，都不会在 X 毫秒内再次触发。【参考方案2】：
这里要注意的重要一点是debounce 产生一个函数，它“封闭”了timeout 变量。 timeout 变量在每次调用生成的函数期间保持可访问性，即使在 debounce 本身返回之后，并且可以切换不同的调用。
debounce 的总体思路如下：
-
开始时没有超时。
如果调用了生成的函数，清除并重置超时。
如果超时，调用原函数。
第一点就是var timeout;，确实就是undefined。幸运的是，clearTimeout 对它的输入相当宽松：传递一个 undefined 计时器标识符会导致它什么也不做，它不会抛出错误或其他什么。
第二点是由produced函数完成的。它首先将有关调用的一些信息（this 上下文和arguments）存储在变量中，以便以后可以将这些信息用于去抖动调用。然后它会清除超时（如果有一组），然后使用setTimeout 创建一个新的来替换它。 请注意，这会覆盖 timeout 的值，并且该值会在多个函数调用中持续存在！ 这允许去抖动实际工作：如果函数被多次调用，timeout 将被多次覆盖一个新的计时器。如果不是这种情况，多个调用将导致启动多个计时器，而 所有 保持活动状态 - 调用只会被延迟，但不会被消除抖动。
第三点在超时回调中完成。它取消设置timeout 变量并使用存储的调用信息进行实际的函数调用。
immediate 标志应该控制是否应该在计时器之前或之后调用该函数。如果是false，则在计时器被击中之后之前不会调用原始函数。如果是true，则首先调用原来的函数，直到定时器被击中才会被调用。
但是，我确实认为 if (immediate && !timeout) 检查是错误的：timeout 刚刚设置为 setTimeout 返回的计时器标识符，因此 !timeout 在那时始终是 false，因此该函数可以永远不会被调用。 The current version of underscore.js 似乎有一个稍微不同的检查，它在调用setTimeout 之前评估immediate && !timeout 之前。 （算法也有点不同，例如它不使用clearTimeout。）这就是为什么您应该始终尝试使用最新版本的库。 :-)
【讨论】：
"请注意，这会覆盖 timeout 的值，并且该值会在多个函数调用中持续存在" 不是每个 debounce 调用的本地超时吗？它是用 var 声明的。每次是如何覆盖的？另外，为什么最后要检查!timeout？为什么不一直存在（因为设置为setTimeout(function() etc.)
@Startec 对于debounce 的每次调用都是本地的，是的，但它在对返回函数的调用之间共享（这是你要调用的函数采用）。例如，在g = debounce(f, 100) 中，timeout 的值会在多次调用g 时保持不变。最后的!timeout检查我相信是一个错误，它不在当前的underscore.js代码中。
为什么超时需要在return函数的早期清除（在它被声明之后）？此外，它会在 setTimeout 函数内部设置为 null。这不是多余的吗？ （首先将其清除，然后将其设置为null。在我使用上述代码的测试中，将 immediate 设置为 true 会使函数根本不调用，正如您所提到的。没有下划线的任何解决方案？【参考方案3】：
去抖函数在调用时不会执行，它们在执行前等待调用暂停超过可配置的持续时间；每次新的调用都会重新启动计时器。
受限制的函数会执行，然后等待一段可配置的持续时间，然后才能再次触发。
去抖动非常适合按键事件；当用户开始输入然后暂停时，您将所有按键作为单个事件提交，从而减少了处理调用。
Throttle 非常适合您只希望允许用户在设定的时间段内调用一次的实时端点。
查看Underscore.js 了解他们的实现。
【讨论】：
【参考方案4】：我写了一篇题为 Demistifying Debounce in JavaScript 的帖子，我在其中准确地解释了 how a debounce function works 并包含了一个演示。
当我第一次遇到去抖功能时，我也没有完全理解它是如何工作的。虽然体积相对较小，但它们实际上采用了一些非常先进的 JavaScript 概念！掌握范围、闭包和setTimeout 方法会有所帮助。
话虽如此，下面是我在上面引用的帖子中解释和演示的基本去抖动功能。
成品
// Create JD Object
// ----------------
var JD = ;
// Debounce Method
// ---------------
JD.debounce = function(func, wait, immediate)
var timeout;
return function()
var context = this,
args = arguments;
var later = function()
timeout = null;
if ( !immediate )
func.apply(context, args);
;
var callNow = immediate && !timeout;
clearTimeout(timeout);
timeout = setTimeout(later, wait || 200);
if ( callNow )
func.apply(context, args);
;
;
解释
// Create JD Object
// ----------------
/*
It's a good idea to attach helper methods like `debounce` to your own
custom object. That way, you don't pollute the global space by
attaching methods to the `window` object and potentially run in to
conflicts.
*/
var JD = ;
// Debounce Method
// ---------------
/*
Return a function, that, as long as it continues to be invoked, will
not be triggered. The function will be called after it stops being
called for `wait` milliseconds. If `immediate` is passed, trigger the
function on the leading edge, instead of the trailing.
*/
JD.debounce = function(func, wait, immediate)
/*
Declare a variable named `timeout` variable that we will later use
to store the *timeout ID returned by the `setTimeout` function.
*When setTimeout is called, it retuns a numeric ID. This unique ID
can be used in conjunction with JavaScript's `clearTimeout` method
to prevent the code passed in the first argument of the `setTimout`
function from being called. Note, this prevention will only occur
if `clearTimeout` is called before the specified number of
milliseconds passed in the second argument of setTimeout have been
met.
*/
var timeout;
/*
Return an anomymous function that has access to the `func`
argument of our `debounce` method through the process of closure.
*/
return function()
/*
1) Assign `this` to a variable named `context` so that the
`func` argument passed to our `debounce` method can be
called in the proper context.
2) Assign all *arugments passed in the `func` argument of our
`debounce` method to a variable named `args`.
*JavaScript natively makes all arguments passed to a function
accessible inside of the function in an array-like variable
named `arguments`. Assinging `arguments` to `args` combines
all arguments passed in the `func` argument of our `debounce`
method in a single variable.
*/
var context = this, /* 1 */
args = arguments; /* 2 */
/*
Assign an anonymous function to a variable named `later`.
This function will be passed in the first argument of the
`setTimeout` function below.
*/
var later = function()
/*
When the `later` function is called, remove the numeric ID
that was assigned to it by the `setTimeout` function.
Note, by the time the `later` function is called, the
`setTimeout` function will have returned a numeric ID to
the `timeout` variable. That numeric ID is removed by
assiging `null` to `timeout`.
*/
timeout = null;
/*
If the boolean value passed in the `immediate` argument
of our `debouce` method is falsy, then invoke the
function passed in the `func` argument of our `debouce`
method using JavaScript's *`apply` method.
*The `apply` method allows you to call a function in an
explicit context. The first argument defines what `this`
should be. The second argument is passed as an array
containing all the arguments that should be passed to
`func` when it is called. Previously, we assigned `this`
to the `context` variable, and we assigned all arguments
passed in `func` to the `args` variable.
*/
if ( !immediate )
func.apply(context, args);
;
/*
If the value passed in the `immediate` argument of our
`debounce` method is truthy and the value assigned to `timeout`
is falsy, then assign `true` to the `callNow` variable.
Otherwise, assign `false` to the `callNow` variable.
*/
var callNow = immediate && !timeout;
/*
As long as the event that our `debounce` method is bound to is
still firing within the `wait` period, remove the numerical ID
(returned to the `timeout` vaiable by `setTimeout`) from
JavaScript's execution queue. This prevents the function passed
in the `setTimeout` function from being invoked.
Remember, the `debounce` method is intended for use on events
that rapidly fire, ie: a window resize or scroll. The *first*
time the event fires, the `timeout` variable has been declared,
but no value has been assigned to it - it is `undefined`.
Therefore, nothing is removed from JavaScript's execution queue
because nothing has been placed in the queue - there is nothing
to clear.
Below, the `timeout` variable is assigned the numerical ID
returned by the `setTimeout` function. So long as *subsequent*
events are fired before the `wait` is met, `timeout` will be
cleared, resulting in the function passed in the `setTimeout`
function being removed from the execution queue. As soon as the
`wait` is met, the function passed in the `setTimeout` function
will execute.
*/
clearTimeout(timeout);
/*
Assign a `setTimout` function to the `timeout` variable we
previously declared. Pass the function assigned to the `later`
variable to the `setTimeout` function, along with the numerical
value assigned to the `wait` argument in our `debounce` method.
If no value is passed to the `wait` argument in our `debounce`
method, pass a value of 200 milliseconds to the `setTimeout`
function.
*/
timeout = setTimeout(later, wait || 200);
/*
Typically, you want the function passed in the `func` argument
of our `debounce` method to execute once *after* the `wait`
period has been met for the event that our `debounce` method is
bound to (the trailing side). However, if you want the function
to execute once *before* the event has finished (on the leading
side), you can pass `true` in the `immediate` argument of our
`debounce` method.
If `true` is passed in the `immediate` argument of our
`debounce` method, the value assigned to the `callNow` variable
declared above will be `true` only after the *first* time the
event that our `debounce` method is bound to has fired.
After the first time the event is fired, the `timeout` variable
will contain a falsey value. Therfore, the result of the
expression that gets assigned to the `callNow` variable is
`true` and the function passed in the `func` argument of our
`debounce` method is exected in the line of code below.
Every subsequent time the event that our `debounce` method is
bound to fires within the `wait` period, the `timeout` variable
holds the numerical ID returned from the `setTimout` function
assigned to it when the previous event was fired, and the
`debounce` method was executed.
This means that for all subsequent events within the `wait`
period, the `timeout` variable holds a truthy value, and the
result of the expression that gets assigned to the `callNow`
variable is `false`. Therefore, the function passed in the
`func` argument of our `debounce` method will not be executed.
Lastly, when the `wait` period is met and the `later` function
that is passed in the `setTimeout` function executes, the
result is that it just assigns `null` to the `timeout`
variable. The `func` argument passed in our `debounce` method
will not be executed because the `if` condition inside the
`later` function fails.
*/
if ( callNow )
func.apply(context, args);
;
;
【讨论】：
最佳解释。谢谢【参考方案5】：我们现在都在使用 Promises
我见过的许多实现都使问题过于复杂或存在其他卫生问题。现在是 2021 年，我们已经使用 Promises 很长时间了——而且有充分的理由。 Promise 清理异步程序并减少发生错误的机会。在这篇文章中，我们将编写自己的debounce。这个实现将 -
我们用它的两个参数编写debounce，task 去抖动，以及延迟的毫秒数，ms。我们为其本地状态引入单个本地绑定，t -
function debounce (task, ms)
let t = promise: null, cancel: _ => void 0
return async (...args) =>
try
t.cancel()
t = deferred(ms)
await t.promise
await task(...args)
catch (_) /* prevent memory leak */
我们依赖于一个可重用的deferred 函数，它创建了一个在ms 毫秒内解析的新承诺。它引入了两个本地绑定，promise 本身，cancel 它的能力 -
function deferred (ms)
let cancel, promise = new Promise((resolve, reject) =>
cancel = reject
setTimeout(resolve, ms)
)
return promise, cancel
点击计数器示例
在第一个示例中，我们有一个计算用户点击次数的按钮。事件侦听器使用debounce 附加，因此计数器仅在指定持续时间后递增 -
// debounce, deferred
function debounce (task, ms) let t = promise: null, cancel: _ => void 0 ; return async (...args) => try t.cancel(); t = deferred(ms); await t.promise; await task(...args); catch (_) console.log("cleaning up cancelled promise")
function deferred (ms) let cancel, promise = new Promise((resolve, reject) => cancel = reject; setTimeout(resolve, ms) ); return promise, cancel
// dom references
const myform = document.forms.myform
const mycounter = myform.mycounter
// event handler
function clickCounter (event)
mycounter.value = Number(mycounter.value) + 1
// debounced listener
myform.myclicker.addEventListener("click", debounce(clickCounter, 1000))<form id="myform">
<input name="myclicker" type="button" value="click" />
<output name="mycounter">0</output>
</form>实时查询示例，“自动完成”
在第二个示例中，我们有一个带有文本输入的表单。我们的search 查询是使用debounce 附加的-
// debounce, deferred
function debounce (task, ms) let t = promise: null, cancel: _ => void 0 ; return async (...args) => try t.cancel(); t = deferred(ms); await t.promise; await task(...args); catch (_) console.log("cleaning up cancelled promise")
function deferred (ms) let cancel, promise = new Promise((resolve, reject) => cancel = reject; setTimeout(resolve, ms) ); return promise, cancel
// dom references
const myform = document.forms.myform
const myresult = myform.myresult
// event handler
function search (event)
myresult.value = `Searching for: $event.target.value`
// debounced listener
myform.myquery.addEventListener("keypress", debounce(search, 1000))<form id="myform">
<input name="myquery" placeholder="Enter a query..." />
<output name="myresult"></output>
</form>【讨论】：
2021年我们不是都在使用Typescript吗？ 不，打字稿是业余爱好者设计类型系统时得到的。编程和技术充满了因各种错误原因而流行的坏事的例子。不要误以为受欢迎是好事。【参考方案6】：你想要做的是：如果你试图一个接一个地调用一个函数，第一个应该被取消，新的应该等待一个给定的超时然后执行。所以实际上你需要某种方式来取消第一个函数的超时？但是怎么做？ 您可以调用该函数，并传递返回的 timeout-id，然后将该 ID 传递给任何新函数。但是上面的解决方案更加优雅。
它的作用是有效地使timeout 变量在返回函数的范围内可用。因此，当触发 'resize' 事件时，它不会再次调用 debounce()，因此 timeout 内容不会更改（！）并且仍然可用于“下一个函数调用”。
这里的关键基本上是每次我们有一个resize事件时我们都会调用内部函数。如果我们想象所有的调整大小事件都在一个数组中，也许会更清楚：
var events = ['resize', 'resize', 'resize'];
var timeout = null;
for (var i = 0; i < events.length; i++)
if (immediate && !timeout) func.apply(this, arguments);
clearTimeout(timeout); // does not do anything if timeout is null.
timeout = setTimeout(function()
timeout = null;
if (!immediate) func.apply(this, arguments);
您看到timeout 可用于下一次迭代吗？
在我看来，没有理由将 this 重命名为 content 和 arguments 重命名为 args。
【讨论】：
“重命名”是绝对必要的。this 和 arguments 的含义在 setTimeout() 回调函数内部发生了变化。您必须在别处保留一份副本，否则该信息将丢失。【参考方案7】：
这是一个变体，它总是在第一次调用时触发去抖动函数，并使用更具描述性的变量：
function debounce(fn, wait = 1000)
let debounced = false;
let resetDebouncedTimeout = null;
return function(...args)
if (!debounced)
debounced = true;
fn(...args);
resetDebouncedTimeout = setTimeout(() =>
debounced = false;
, wait);
else
clearTimeout(resetDebouncedTimeout);
resetDebouncedTimeout = setTimeout(() =>
debounced = false;
fn(...args);
, wait);
;
【讨论】：
【参考方案8】：javascript中的简单去抖动方法
<!-- Basic html -->
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width">
<title>Debounce Method</title>
</head>
<body>
<button type="button" id="debounce">Debounce Method</button><br />
<span id="message"></span>
</body>
</html>
// JS File
var debouncebtn = document.getElementById('debounce');
function debounce(func, delay)
var debounceTimer;
return function ()
var context = this, args = arguments;
clearTimeout(debounceTimer);
debounceTimer = setTimeout(function()
func.apply(context, args)
, delay);
// Driver Code
debouncebtn.addEventListener('click', debounce(function()
document.getElementById('message').innerHTML += '<br/> Button only triggeres is every 3 secounds how much every you fire an event';
console.log('Button only triggeres in every 3 secounds how much every you fire an event');
,3000))
运行时示例 JSFiddle：https://jsfiddle.net/arbaazshaikh919/d7543wqe/10/
【讨论】：
不幸的是，我无法从部分 args = arguments 中理解。论据从何而来？我认为您需要将其设置为返回函数的参数【参考方案9】：简单的去抖动功能：-
HTML:-
<button id='myid'>Click me</button>
Javascript:-
function debounce(fn, delay)
let timeoutID;
return function(...args)
if(timeoutID) clearTimeout(timeoutID);
timeoutID = setTimeout(()=>
fn(...args)
, delay);
document.getElementById('myid').addEventListener('click', debounce(() =>
console.log('clicked');
,2000));
【讨论】：
【参考方案10】：下面是debounce 函数作用的摘要，用几行演示解释。
debounce 函数是这样的函数：
clearTimeOut函数）
重新安排一个新的（使用setTimeout 函数）
并且循环一直持续到时间间隔过去并且包装的函数执行。
改编自所有 cmets 和 this article
function debounce(callBack, interval, leadingExecution)
// the schedule identifier, if it's not null/undefined, a callBack function was scheduled
let timerId;
return function ()
// Does the previous run has schedule a run
let wasFunctionScheduled = (typeof timerId === 'number');
// Delete the previous run (if timerId is null, it does nothing)
clearTimeout(timerId);
// Capture the environment (this and argument) and wraps the callback function
let funcToDebounceThis = this, funcToDebounceArgs = arguments;
let funcToSchedule = function ()
// Reset/delete the schedule
clearTimeout(timerId);
timerId = null;
// trailing execution happens at the end of the interval
if (!leadingExecution)
// Call the original function with apply
callBack.apply(funcToDebounceThis, funcToDebounceArgs);
// Schedule a new execution at each execution
timerId = setTimeout(funcToSchedule, interval);
// Leading execution
if (!wasFunctionScheduled && leadingExecution) callBack.apply(funcToDebounceThis, funcToDebounceArgs);
function onMouseMove(e)
console.log(new Date().toLocaleString() + ": Position: x: " + e.x + ", y:" + e.y);
let debouncedMouseMove = debounce(onMouseMove, 500);
document.addEventListener('mousemove', debouncedMouseMove);【讨论】：
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