html
```html
<div id="content" style="height:150px;line-height:150px;text-align:center; color: #fff;background-color:#ccc;font-size:80px;"></div>
<script>
let num = 1;
let content = document.getElementById('content');
function count() {
content.innerHTML = num++;
};
content.onmousemove = count;
</script>
```
## 防抖(debounce)
**所謂防抖,就是指觸發事件后在 n 秒內函數只能執行一次,如果在 n 秒內又觸發了事件,則會重新計算函數執行時間。**
防抖函數分為非立即執行版和立即執行版。
### 非立即執行版:
```javascript
function debounce(func, wait) {
let timeout;
return function () {
let context = this;
let args = arguments;
if (timeout) clearTimeout(timeout);
timeout = setTimeout(() => {
func.apply(context, args)
}, wait);
}
}
```
使用方式
```javascript
content.onmousemove = debounce(count,1000);
```
### 立即執行版:
```javascript
function debounce(func,wait) {
let timeout;
return function () {
let context = this;
let args = arguments;
if (timeout) clearTimeout(timeout);
let callNow = !timeout;
timeout = setTimeout(() => {
timeout = null;
}, wait)
if (callNow) func.apply(context, args)
}
}
```
### 合并版
```javascript
/**
* @desc 函數防抖
* @param func 函數
* @param wait 延遲執行毫秒數
* @param immediate true 表立即執行,false 表非立即執行
*/
function debounce(func,wait,immediate) {
let timeout;
return function () {
let context = this;
let args = arguments;
if (timeout) clearTimeout(timeout);
if (immediate) {
var callNow = !timeout;
timeout = setTimeout(() => {
timeout = null;
}, wait)
if (callNow) func.apply(context, args)
}
else {
timeout = setTimeout(function(){
func.apply(context, args)
}, wait);
}
}
}
```
## 節流(throttle)
**所謂節流,就是指連續觸發事件但是在 n 秒中只執行一次函數。**節流會稀釋函數的執行頻率。
對于節流,一般有兩種方式可以實現,分別是時間戳版和定時器版。
### 時間戳版:
```javascript
function throttle(func, wait) {
let previous = 0;
return function() {
let now = Date.now();
let context = this;
let args = arguments;
if (now - previous > wait) {
func.apply(context, args);
previous = now;
}
}
}
```
使用方式
```javascript
content.onmousemove = throttle(count,1000);
```
### 定時器版:
```javascript
function throttle(func, wait) {
let timeout;
return function() {
let context = this;
let args = arguments;
if (!timeout) {
timeout = setTimeout(() => {
timeout = null;
func.apply(context, args)
}, wait)
}
}
}
```
### 合并版:
```javascript
/**
* @desc 函數節流
* @param func 函數
* @param wait 延遲執行毫秒數
* @param type 1 表時間戳版,2 表定時器版
*/
function throttle(func, wait ,type) {
if(type===1){
let previous = 0;
}else if(type===2){
let timeout;
}
return function() {
let context = this;
let args = arguments;
if(type===1){
let now = Date.now();
if (now - previous > wait) {
func.apply(context, args);
previous = now;
}
}else if(type===2){
if (!timeout) {
timeout = setTimeout(() => {
timeout = null;
func.apply(context, args)
}, wait)
}
}
}
}
```
[https://github.com/mqyqingfeng/Blog/issues/22](https://github.com/mqyqingfeng/Blog/issues/22)
[https://github.com/mqyqingfeng/Blog/issues/26](https://github.com/mqyqingfeng/Blog/issues/26)