React中使用防抖函数和节流函数
在React事件调用时，React传递给事件处理程序是一个合成事件对象的实例。SyntheticEvent对象是通过合并得到的。 这意味着在事件回调被调用后，SyntheticEvent 对象将被重用并且所有属性都将被取消。 这是出于性能原因。 因此，您无法以异步方式访问该事件。React合成事件官方文档
所以在用防抖或节流函数封装时，异步方式访问事件对象出现问题。解决的方法如下：
方法一：调用合成事件对象的persist()方法 event.persist && event.persist() //保留对事件的引用
方法二：深拷贝事件对象 const event = e && {...e} //深拷贝事件对象
function debounce(func, wait=500) {
let timeout; // 定时器变量
return function(event){
clearTimeout(timeout); // 每次触发时先清除上一次的定时器,然后重新计时
event.persist && event.persist() //保留对事件的引用
//const event = e && {...e} //深拷贝事件对象
timeout = setTimeout(()=>{
func(event)
}, wait); // 指定 xx ms 后触发真正想进行的操作 handler
};
}
防抖debounce
防抖 Debounce 多次触发，只在最后一次触发时，执行目标函数。
函数防抖就是，延迟一段时间再执行函数，如果这段时间内又触发了该函数，则延迟重新计算。
应用场景
（1）通过监听某些事件完成对应的需求，比如：
通过监听 scroll 事件，检测滚动位置，根据滚动位置显示返回顶部按钮
通过监听 resize 事件，对某些自适应页面调整DOM的渲染（通过CSS实现的自适应不再此范围内）
通过监听 keyup 事件，监听文字输入并调用接口进行模糊匹配
（2）其他场景
表单组件输入内容验证
防止多次点击导致表单多次提交
简单实现
function debounce(fn, wait) {
let t
return () => {
let context = this
let args = arguments
if (t) clearTimeout(t)
t= setTimeout(() => {
fn.apply(context, args)
}, wait)
}
}
完整实现
function debounce(func, wait, immediate) {
let time;
let debounced = function() {
let context = this;
if(time) clearTimeout(time);
if(immediate) {
let callNow = !time;
if(callNow) func.apply(context, arguments);
time = setTimeout(
()=>{time = null} //见注解
, wait)
} else {
time = setTimeout(
()=>{func.apply(context, arguments)}
, wait)
}
};
debounced.cancel = function() {
clearTimeout(time);
time = null
};
return debounced
}
// underscore.js debounce
//
// 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. If `immediate` is passed, trigger the function on the
// leading edge, instead of the trailing.
_.debounce = function(func, wait, immediate) {
var timeout, args, context, timestamp, result;
// 处理时间
var later = function() {
var last = _.now() - timestamp;
if (last < wait && last >= 0) {
timeout = setTimeout(later, wait - last); // 10ms 6ms 4ms
} else {
timeout = null;
if (!immediate) {
result = func.apply(context, args);
if (!timeout) context = args = null;
}
}
};
react中调用方法
this.handleGetCustomerNameList = debounce(this.handleGetCustomerNameList.bind(this), 500);
节流 throttle
节流：函数间隔一段时间后才能再触发，避免某些函数触发频率过高，比如滚动条滚动事件触发的函数。
### 简单实现
function throttle (fn, wait, mustRun) {
let start = new Date()
let timeout
return () => {
// 在返回的函数内部保留上下文和参数
let context = this
let args = arguments
let current = new Date()
clearTimeout(timeout)
let remaining = current - start
// 达到了指定触发时间，触发该函数
if (remaining > mustRun) {
fn.apply(context, args)
start = current
} else {
// 否则wait时间后触发，闭包保留一个timeout实例
timeout = setTimeout(fn, wait);
}
}
}
完整实现
function throttle(func, wait, options) {
let time, context, args, result;
let previous = 0;
if (!options) options = {};
let later = function () {
previous = options.leading === false ? 0 : new Date().getTime();
time = null;
func.apply(context, args);
if (!time) context = args = null;
};
let throttled = function () {
let now = new Date().getTime();
if (!previous && options.leading === false) previous = now;
let remaining = wait - (now - previous);
context = this;
args = arguments;
if (remaining <= 0 || remaining > wait) {
if (time) {
clearTimeout(time);
time = null;
}
previous = now;
func.apply(context, args);
if (!time) context = args = null;
} else if (!time && options.trailing !== false) {
time = setTimeout(later, remaining);
}
};
return throttled;
}
// underscore.js throttle
// Returns a function, that, when invoked, will only be triggered at most once
// during a given window of time. Normally, the throttled function will run
// as much as it can, without ever going more than once per `wait` duration;
// but if you'd like to disable the execution on the leading edge, pass
// `{leading: false}`. To disable execution on the trailing edge, ditto.
_.throttle = function(func, wait, options) {
var context, args, result;
var timeout = null;
var previous = 0;
if (!options) options = {};
var later = function() {
previous = options.leading === false ? 0 : _.now();
timeout = null;
result = func.apply(context, args);
if (!timeout) context = args = null;
};
return function() {
var now = _.now();
if (!previous && options.leading === false) previous = now;
var remaining = wait - (now - previous);
context = this;
args = arguments;
if (remaining <= 0 || remaining > wait) {
if (timeout) {
clearTimeout(timeout);
timeout = null;
}
previous = now;
result = func.apply(context, args);
if (!timeout) context = args = null;
} else if (!timeout && options.trailing !== false) {
timeout = setTimeout(later, remaining);
}
return result;
};
};
react中调用方法
this.handleGetCustomerNameList = throttle (this.handleGetCustomerNameList.bind(this), 500);
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