连续操作：两个操作之间的时间间隔小于设定的阀值，这样子的一连串操作视为连续操作。
debounce（防抖）：一个连续操作中的处理，只触发一次，从而实现防抖动。
throttle：一个连续操作中的处理，按照阀值时间间隔进行触发，从而实现节流。
发生的情况:
- a、scroll事件：当页面发生滚动时，scroll事件会被频繁的触发，1s触发可高达上百次。在scroll事件中，如果有复杂的操作（特别是影响布局的操作），将会大大影响性能，甚至导致浏览器崩溃。所以，对其进行防抖、限频很重要。
- b、click事件：用户进行click事件时，有可能连续触发点击（用户本意并非双击）。该操作有可能是不小心多次连续点击，也可能是页面状况不好的情况下，期待尽快得到反馈的有意行为；但这样的操作，反而会加剧性能问题，因此也有必要考虑防抖、限频。
- c、input事件：如sug等需要通过ajax及时获得数据的情况，需要进行限频，防止频繁的请求发生，减少服务器压力的同时，提高页面响应性能。
- d、touchmove事件：同scroll事件类似。
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<style>
.box {
height: 500px;
overflow: scroll;
width: 200px;
}
.box img {
height: 200px;
}
</style>
<body>
<button id="btn">
点击
</button>
<div class="box" id="imgBox">
<img src="https://ss2.bdstatic.com/70cFvnSh_Q1YnxGkpoWK1HF6hhy/it/u=2442489277,908091175&fm=26&gp=0.jpg" alt="">
<img src="https://ss2.bdstatic.com/70cFvnSh_Q1YnxGkpoWK1HF6hhy/it/u=2442489277,908091175&fm=26&gp=0.jpg" alt="">
<img src="https://ss2.bdstatic.com/70cFvnSh_Q1YnxGkpoWK1HF6hhy/it/u=2442489277,908091175&fm=26&gp=0.jpg" alt="">
<img src="https://ss2.bdstatic.com/70cFvnSh_Q1YnxGkpoWK1HF6hhy/it/u=2442489277,908091175&fm=26&gp=0.jpg" alt="">
<img src="https://ss2.bdstatic.com/70cFvnSh_Q1YnxGkpoWK1HF6hhy/it/u=2442489277,908091175&fm=26&gp=0.jpg" alt="">
</div>
</body>
<script>
document.getElementById('imgBox').addEventListener('scroll', throttle(100, () => {
console.log(1111111);
}, true));
const btn = document.getElementById('btn')
btn.addEventListener('click', throttle(100, () => {
btn.setAttribute('disabled', true)
}, false))
// document.getElementById('imgBox').addEventListener('scroll', () => {
// console.log(1111111);
// });
/* eslint-disable no-undefined,no-param-reassign,no-shadow */
/**
* Throttle execution of a function. Especially useful for rate limiting
* execution of handlers on events like resize and scroll.
*
* @param {Number} delay A zero-or-greater delay in milliseconds. For event callbacks, values around 100 or 250 (or even higher) are most useful.
* @param {Boolean} [noTrailing] Optional, defaults to false. If noTrailing is true, callback will only execute every `delay` milliseconds while the
* throttled-function is being called. If noTrailing is false or unspecified, callback will be executed one final time
* after the last throttled-function call. (After the throttled-function has not been called for `delay` milliseconds,
* the internal counter is reset)
* @param {Function} callback A function to be executed after delay milliseconds. The `this` context and all arguments are passed through, as-is,
* to `callback` when the throttled-function is executed.
* @param {Boolean} [debounceMode] If `debounceMode` is true (at begin), schedule `clear` to execute after `delay` ms. If `debounceMode` is false (at end),
* schedule `callback` to execute after `delay` ms.
*
* @return {Function} A new, throttled, function.
*/
function throttle(delay, noTrailing, callback, debounceMode) {
// After wrapper has stopped being called, this timeout ensures that
// `callback` is executed at the proper times in `throttle` and `end`
// debounce modes.
var timeoutID;
// Keep track of the last time `callback` was executed.
var lastExec = 0;
// `noTrailing` defaults to falsy.
if (typeof noTrailing !== 'boolean') {
debounceMode = callback;
callback = noTrailing;
noTrailing = undefined;
}
// The `wrapper` function encapsulates all of the throttling / debouncing
// functionality and when executed will limit the rate at which `callback`
// is executed.
function wrapper() {
var self = this;
var elapsed = Number(new Date()) - lastExec;
var args = arguments;
// Execute `callback` and update the `lastExec` timestamp.
function exec() {
lastExec = Number(new Date());
callback.apply(self, args);
}
// If `debounceMode` is true (at begin) this is used to clear the flag
// to allow future `callback` executions.
function clear() {
timeoutID = undefined;
}
if (debounceMode && !timeoutID) {
// Since `wrapper` is being called for the first time and
// `debounceMode` is true (at begin), execute `callback`.
exec();
}
// Clear any existing timeout.
if (timeoutID) {
clearTimeout(timeoutID);
}
if (debounceMode === undefined && elapsed > delay) {
// In throttle mode, if `delay` time has been exceeded, execute
// `callback`.
exec();
} else if (noTrailing !== true) {
// In trailing throttle mode, since `delay` time has not been
// exceeded, schedule `callback` to execute `delay` ms after most
// recent execution.
//
// If `debounceMode` is true (at begin), schedule `clear` to execute
// after `delay` ms.
//
// If `debounceMode` is false (at end), schedule `callback` to
// execute after `delay` ms.
timeoutID = setTimeout(debounceMode ? clear : exec, debounceMode === undefined ? delay - elapsed :
delay);
}
}
// Return the wrapper function.
return wrapper;
};
</script>
</html>
