React中使用防抖函數和節流函數
在React事件調用時，React傳遞給事件處理程序是一個合成事件對象的實例。SyntheticEvent對象是通過合并得到的。 這意味著在事件回調被調用后，SyntheticEvent 對象將被重用并且所有屬性都將被取消。 這是出于性能原因。 因此，您無法以異步方式訪問該事件。React合成事件官方文檔
所以在用防抖或節流函數封裝時，異步方式訪問事件對象出現問題。解決的方法如下：
方法一：調用合成事件對象的persist()方法 event.persist && event.persist() //保留對事件的引用
方法二：深拷貝事件對象 const event = e && {...e} //深拷貝事件對象
function debounce(func, wait=500) {let timeout; // 定時器變量return function(event){clearTimeout(timeout); // 每次觸發時先清除上一次的定時器,然后重新計時event.persist && event.persist() //保留對事件的引用//const event = e && {...e} //深拷貝事件對象timeout = setTimeout(()=>{func(event)}, wait); // 指定 xx ms 后觸發真正想進行的操作 handler};}防抖debounce
防抖 Debounce 多次觸發，只在最后一次觸發時，執行目標函數。
函數防抖就是，延遲一段時間再執行函數，如果這段時間內又觸發了該函數，則延遲重新計算。
應用場景
（1）通過監聽某些事件完成對應的需求，比如：
通過監聽 scroll 事件，檢測滾動位置，根據滾動位置顯示返回頂部按鈕
通過監聽 resize 事件，對某些自適應頁面調整DOM的渲染（通過CSS實現的自適應不再此范圍內）
通過監聽 keyup 事件，監聽文字輸入并調用接口進行模糊匹配
（2）其他場景
表單組件輸入內容驗證
防止多次點擊導致表單多次提交
簡單實現
function debounce(fn, wait) {let treturn () => {let context = thislet args = argumentsif (t) clearTimeout(t)t= setTimeout(() => {fn.apply(context, args)}, wait)}}完整實現
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} //見注解, 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;// 處理時間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中調用方法
this.handleGetCustomerNameList = debounce(this.handleGetCustomerNameList.bind(this), 500);
節流 throttle
節流：函數間隔一段時間后才能再觸發，避免某些函數觸發頻率過高，比如滾動條滾動事件觸發的函數。
### 簡單實現function throttle (fn, wait, mustRun) {let start = new Date()let timeoutreturn () => {// 在返回的函數內部保留上下文和參數let context = thislet args = argumentslet current = new Date()clearTimeout(timeout)let remaining = current - start// 達到了指定觸發時間，觸發該函數if (remaining > mustRun) {fn.apply(context, args)start = current} else {// 否則wait時間后觸發，閉包保留一個timeout實例timeout = setTimeout(fn, wait);}}}完整實現
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中調用方法
this.handleGetCustomerNameList = throttle (this.handleGetCustomerNameList.bind(this), 500);
以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持VeVb武林網。
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