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JavaScript 的性能優化：加載和執行

概覽無論當前JavaScript代碼是內嵌還是在外鏈文件中，頁面的下載和渲染都必須停下來等待腳本執行完成。JavaScript執行過程耗時越久，瀏覽器等待響應用戶輸入的時間就越長。瀏覽器在下載和執行腳本時出現阻塞的原因在于，腳本可能會改變頁面或JavaScript的命名空間，它們對后面頁面內容造成影響。一個典型的例子就是在頁面中使用document.write()。例如清單1清單1JavaScript代碼內嵌示例Sou</span> <p class="auth-span"> <span id="tjgufvlx2j" class="muted"><i class="fa fa-user"></i><span id="tjgufvlx2j" class="zj-icon-text">系統</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-clock-o"></i><span id="tjgufvlx2j" class="zj-icon-text">2019-08-29 22:50:45</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-eye"></i><span id="tjgufvlx2j" class="zj-icon-text">2669</span></span>  </p> </article><article class="excerpt"> <header> <a title="Javascript" class="label label-important zj-del-target" href="/category/66">Javascript<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/539" title="Javascript的聲明" target="_blank" onclick="return recordId('cid',66)">Javascript的聲明 </a> </h2> </header> <div id="tjgufvlx2j" class="focus"> <a class="zj-del-target" href="/article/539" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/11.jpg" alt="" title=""></a> </div> <span id="tjgufvlx2j" class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/539';}else{window.open('/article/539');}" style="cursor: pointer;">Quiz下面Javascript代碼為什么能運行？hello();functionhello(){alert("Hello,world!");}但對于C，這么寫會報錯：#include"stdio.h"voidmain(){hello();}voidhello(){printf("Hello,world\n");}由于hello沒有被預先聲明，代碼“hello()”被認為是隱式聲明，而隱式聲明返回類型是int，所以提示hello類型錯誤。通過預先聲明或者將</span> <p class="auth-span"> <span id="tjgufvlx2j" class="muted"><i class="fa fa-user"></i><span id="tjgufvlx2j" class="zj-icon-text">系統</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-clock-o"></i><span id="tjgufvlx2j" class="zj-icon-text">2019-08-12 01:32:08</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-eye"></i><span id="tjgufvlx2j" class="zj-icon-text">2669</span></span>  </p> </article><article class="excerpt"> <header> <a title="Javascript" class="label label-important zj-del-target" href="/category/66">Javascript<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/3742" title="一種模仿線程的Javascript異步模型設計&實現" target="_blank" onclick="return recordId('cid',66)">一種模仿線程的Javascript異步模型設計&實現 </a> </h2> </header> <div id="tjgufvlx2j" class="focus"> <a class="zj-del-target" href="/article/3742" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/6.jpg" alt="" title=""></a> </div> <span id="tjgufvlx2j" class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/3742';}else{window.open('/article/3742');}" style="cursor: pointer;">jQuery中所支持的異步模型為：Callbacks，回調函數列隊。Deferred，延遲執行對象。Promise，是Deferred只暴露非狀態改變方法的對象。這些模型都很漂亮，但我想要一種更帥氣的異步模型。Thread？我們知道鏈式操作是可以很好的表征運行順序的（可以參考我的文章《jQuery鏈式操作》），然而通常基于回調函數或者基于事件監聽的異步模型中，代碼的執行順序不清晰。Callbacks模型實際上類似一個自定義事件的回調函數隊列，當觸發該事件（</span> <p class="auth-span"> <span id="tjgufvlx2j" class="muted"><i class="fa fa-user"></i><span id="tjgufvlx2j" class="zj-icon-text">系統</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-clock-o"></i><span id="tjgufvlx2j" class="zj-icon-text">2019-08-12 01:33:28</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-eye"></i><span id="tjgufvlx2j" class="zj-icon-text">2668</span></span>  </p> </article><article class="excerpt"> <header> <a title="Javascript" class="label label-important zj-del-target" href="/category/66">Javascript<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/17143" title="JavaScript遞歸" target="_blank" onclick="return recordId('cid',66)">JavaScript遞歸 </a> </h2> </header> <div id="tjgufvlx2j" class="focus"> <a class="zj-del-target" href="/article/17143" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/11.jpg" alt="" title=""></a> </div> <span id="tjgufvlx2j" class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/17143';}else{window.open('/article/17143');}" style="cursor: pointer;">ServerSideJavaScriptwithASPcode/**//***ClassNavigator*@authorKimSoft*@versionbuild2006-07-0917:46*@copyright2006KimSoftAllRightsReserved.*/functionNavigator(boardId)...{this._boardId=boardId;this._db=$singleton(function()...{retur</span> <p class="auth-span"> <span id="tjgufvlx2j" class="muted"><i class="fa fa-user"></i><span id="tjgufvlx2j" class="zj-icon-text">系統</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-clock-o"></i><span id="tjgufvlx2j" class="zj-icon-text">2019-08-29 22:50:07</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-eye"></i><span id="tjgufvlx2j" class="zj-icon-text">2666</span></span>  </p> </article><article class="excerpt"> <header> <a title="Javascript" class="label label-important zj-del-target" href="/category/66">Javascript<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/14012" title="eclipse Errors running builder 'JavaScript V" target="_blank" onclick="return recordId('cid',66)">eclipse Errors running builder 'JavaScript V </a> </h2> </header> <div id="tjgufvlx2j" class="focus"> <a class="zj-del-target" href="/article/14012" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/16.jpg" alt="" title=""></a> </div> <span id="tjgufvlx2j" class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/14012';}else{window.open('/article/14012');}" style="cursor: pointer;">跑java程序時提示錯誤：Errorsoccurredduringthebuild.Errorsrunningbuilder'JavaScriptValidator'onproject'......'.java.lang.NullPointerException導致計算機運行速度很慢，因此想取消關于js校驗的工作。提高eclipse運行的速度。解決方法：項目—-右鍵Properties—-Builders—-取消“JavaScriptValidator”e</span> <p class="auth-span"> <span id="tjgufvlx2j" class="muted"><i class="fa fa-user"></i><span id="tjgufvlx2j" class="zj-icon-text">系統</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-clock-o"></i><span id="tjgufvlx2j" class="zj-icon-text">2019-08-29 22:10:45</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-eye"></i><span id="tjgufvlx2j" class="zj-icon-text">2666</span></span>  </p> </article><article class="excerpt"> <header> <a title="Javascript" class="label label-important zj-del-target" href="/category/66">Javascript<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/11029" title="Javascript 操作select控件大全（新增、修改、" target="_blank" onclick="return recordId('cid',66)">Javascript 操作select控件大全（新增、修改、 </a> </h2> </header> <div id="tjgufvlx2j" class="focus"> <a class="zj-del-target" href="/article/11029" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/12.jpg" alt="" title=""></a> </div> <span id="tjgufvlx2j" class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/11029';}else{window.open('/article/11029');}" style="cursor: pointer;">Javascript操作select控件大全（新增、修改、刪除、選中、清空、判斷存在等）Postedon2007-08-0814:56禮拜一閱讀(14918)評論(28)編輯收藏網摘所屬分類:JavaScript1判斷select選項中是否存在Value="paraValue"的Item2向select選項中加入一個Item3從select選項中刪除一個Item4刪除select中選中的項5修改select選項中value="paraValu</span> <p class="auth-span"> <span id="tjgufvlx2j" class="muted"><i class="fa fa-user"></i><span id="tjgufvlx2j" class="zj-icon-text">系統</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-clock-o"></i><span id="tjgufvlx2j" class="zj-icon-text">2019-08-12 09:29:29</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-eye"></i><span id="tjgufvlx2j" class="zj-icon-text">2665</span></span>  </p> </article><article class="excerpt"> <header> <a title="Javascript" class="label label-important zj-del-target" href="/category/66">Javascript<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/17534" title="10款Flash和Javascript網頁音樂播放器" target="_blank" onclick="return recordId('cid',66)">10款Flash和Javascript網頁音樂播放器 </a> </h2> </header> <div id="tjgufvlx2j" class="focus"> <a class="zj-del-target" href="/article/17534" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/14.jpg" alt="" title=""></a> </div> <span id="tjgufvlx2j" class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/17534';}else{window.open('/article/17534');}" style="cursor: pointer;">關聯：9FreshjQueryMediaPlayers10款音樂播放器，有基于javascript的網頁音樂播放器，也有基于Flash的音樂播放器。趕快挑一款，分享你喜愛的音樂吧！1.DewplayerDewplayer是一個微型，免費的Flashmp3播放器，具有簡潔的界面。Dewplayer包含三種不同的尺寸界面。2.NiftyPlayerNiftyPlayer是一個非常小（4KB），開源的FlashMP3播放器。擁有非常簡潔的界面。可以利用JavaS</span> <p class="auth-span"> <span id="tjgufvlx2j" class="muted"><i class="fa fa-user"></i><span id="tjgufvlx2j" class="zj-icon-text">系統</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-clock-o"></i><span id="tjgufvlx2j" class="zj-icon-text">2019-08-29 22:54:57</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-eye"></i><span id="tjgufvlx2j" class="zj-icon-text">2664</span></span>  </p> </article><article class="excerpt"> <header> <a title="Javascript" class="label label-important zj-del-target" href="/category/66">Javascript<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/13836" title="JavaScript 計時器,倒計時" target="_blank" onclick="return recordId('cid',66)">JavaScript 計時器,倒計時 </a> </h2> </header> <div id="tjgufvlx2j" class="focus"> <a class="zj-del-target" href="/article/13836" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/12.jpg" alt="" title=""></a> </div> <span id="tjgufvlx2j" class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/13836';}else{window.open('/article/13836');}" style="cursor: pointer;">先看效果//列表的的效果//單個效果varbjtimer={sysTime:0,//服務器時間毫秒數timeBodyName:"timecontainer",//顯示時間的容器timeBodyTag:"div",showFmt:"dd天HH時mm分ss秒",notstartMsg:"即將開始:",startingMsg:"剩余時間:",afterStart:"活動進行中",//開始后的內容afterEnd:"活動已結束",//結束后是否設置提示內容stim</span> <p class="auth-span"> <span id="tjgufvlx2j" class="muted"><i class="fa fa-user"></i><span id="tjgufvlx2j" class="zj-icon-text">系統</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-clock-o"></i><span id="tjgufvlx2j" class="zj-icon-text">2019-08-29 22:08:39</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-eye"></i><span id="tjgufvlx2j" class="zj-icon-text">2664</span></span>  </p> </article><article class="excerpt"> <header> <a title="Javascript" class="label label-important zj-del-target" href="/category/66">Javascript<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/11018" title="用 JavaScript 創建模塊化的交互用戶界面" target="_blank" onclick="return recordId('cid',66)">用 JavaScript 創建模塊化的交互用戶界面 </a> </h2> </header> <div id="tjgufvlx2j" class="focus"> <a class="zj-del-target" href="/article/11018" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/10.jpg" alt="" title=""></a> </div> <span id="tjgufvlx2j" class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/11018';}else{window.open('/article/11018');}" style="cursor: pointer;">級別：中級GregTravis,軟件工程師2008年10月28日通過本文，了解使用拖放功能移動Web頁面的不同部分的技巧。分別實現交互性的不同方面，然后再將它們組合在一起，這樣便于靈活定制頁面，也讓您的Web用戶非常滿意。JavaScript是一種功能強大的語言，可用于創建基于Web的應用程序。它已經足夠穩定和成熟，完全可以創建與傳統桌面應用程序相抗衡的程序，因為后者在穩定性和特性豐富性方面都要勝出一籌。但JavaScript最初只是用來向靜態Web頁面添</span> <p class="auth-span"> <span id="tjgufvlx2j" class="muted"><i class="fa fa-user"></i><span id="tjgufvlx2j" class="zj-icon-text">系統</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-clock-o"></i><span id="tjgufvlx2j" class="zj-icon-text">2019-08-12 09:29:29</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-eye"></i><span id="tjgufvlx2j" class="zj-icon-text">2664</span></span>  </p> </article><article class="excerpt"> <header> <a title="Javascript" class="label label-important zj-del-target" href="/category/66">Javascript<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/4126" title="Javascript圖像處理——圖像金字塔" target="_blank" onclick="return recordId('cid',66)">Javascript圖像處理——圖像金字塔 </a> </h2> </header> <div id="tjgufvlx2j" class="focus"> <a class="zj-del-target" href="/article/4126" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/10.jpg" alt="" title=""></a> </div> <span id="tjgufvlx2j" class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/4126';}else{window.open('/article/4126');}" style="cursor: pointer;">前言上一篇文章，我們講解了邊緣梯度計算函數，這篇文章我們來了解圖像金字塔。圖像金字塔？圖像金字塔被廣泛用于計算機視覺應用中。圖像金字塔是一個圖像集合，集合中所有的圖像都源于同一個原始圖像，而且是通過對原始圖像連續降采樣獲得的。——《學習OpenCV》常見的圖像金字塔有下面兩種：高斯金字塔(Gaussianpyramid):用來向下采樣拉普拉斯金字塔(Laplacianpyramid):用來從金字塔低層圖像重建上層未采樣圖像高斯金字塔類似金字塔一樣，高斯金字</span> <p class="auth-span"> <span id="tjgufvlx2j" class="muted"><i class="fa fa-user"></i><span id="tjgufvlx2j" class="zj-icon-text">系統</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-clock-o"></i><span id="tjgufvlx2j" class="zj-icon-text">2019-08-12 01:33:37</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-eye"></i><span id="tjgufvlx2j" class="zj-icon-text">2663</span></span>  </p> </article><article class="excerpt"> <header> <a title="Javascript" class="label label-important zj-del-target" href="/category/66">Javascript<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/420" title="Javascript圖像處理——閾值" target="_blank" onclick="return recordId('cid',66)">Javascript圖像處理——閾值 </a> </h2> </header> <div id="tjgufvlx2j" class="focus"> <a class="zj-del-target" href="/article/420" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/6.jpg" alt="" title=""></a> </div> <span id="tjgufvlx2j" class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/420';}else{window.open('/article/420');}" style="cursor: pointer;">前言上一篇文章，我們講解了圖像處理中的亮度和對比度的變化，這篇文章我們來做一個閾值函數。最簡單的圖像分割方法閾值是最簡單的圖像分割方法。比如為了從下圖中分割出蘋果，我們利用前景與背景的灰度差值，通過設定一個閾值，對于該像素大于這個閾值時就以黑色表示，小于便以灰色表示。五種閾值類型和OpenCV一樣，我們將提供五種閾值類型，方便使用。下面是原圖像的波形表示，縱坐標表示像素點的灰度值大小，藍線是閾值大小。二進制閾值化公式表示是：圖像表示是：可見超過該閾值的就變</span> <p class="auth-span"> <span id="tjgufvlx2j" class="muted"><i class="fa fa-user"></i><span id="tjgufvlx2j" class="zj-icon-text">系統</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-clock-o"></i><span id="tjgufvlx2j" class="zj-icon-text">2019-08-12 01:32:03</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-eye"></i><span id="tjgufvlx2j" class="zj-icon-text">2663</span></span>  </p> </article><article class="excerpt"> <header> <a title="Javascript" class="label label-important zj-del-target" href="/category/66">Javascript<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/4580" title="JavaScript 語言基礎知識點總結（思維導圖）" target="_blank" onclick="return recordId('cid',66)">JavaScript 語言基礎知識點總結（思維導圖） </a> </h2> </header> <div id="tjgufvlx2j" class="focus"> <a class="zj-del-target" href="/article/4580" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/10.jpg" alt="" title=""></a> </div> <span id="tjgufvlx2j" class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/4580';}else{window.open('/article/4580');}" style="cursor: pointer;">JavaScript數組JavaScript函數基礎Javascript運算符JavaScript流程控制JavaScript正則表達式JavaScript字符串函數JavaScript數據類型JavaScript變量Window對象DOM基本操作JavaScript語言基礎知識點總結（思維導圖）</span> <p class="auth-span"> <span id="tjgufvlx2j" class="muted"><i class="fa fa-user"></i><span id="tjgufvlx2j" class="zj-icon-text">系統</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-clock-o"></i><span id="tjgufvlx2j" class="zj-icon-text">2019-08-12 01:33:49</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-eye"></i><span id="tjgufvlx2j" class="zj-icon-text">2659</span></span>  </p> </article><article class="excerpt"> <header> <a title="Javascript" class="label label-important zj-del-target" href="/category/66">Javascript<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/20435" title="用JavaScript獲取頁面上被選中的文字的技巧" target="_blank" onclick="return recordId('cid',66)">用JavaScript獲取頁面上被選中的文字的技巧 </a> </h2> </header> <div id="tjgufvlx2j" class="focus"> <a class="zj-del-target" href="/article/20435" target="_blank"><img style="width: 200px; height: 123px;" class="thumb" src="/Public/static/images/article/12.jpg" alt="" title=""></a> </div> <span id="tjgufvlx2j" class="note" onclick="if (jq.browser.versions.mobile) {window.location.href='/article/20435';}else{window.open('/article/20435');}" style="cursor: pointer;">這里介紹的一個小技巧是如何用JavaScript獲取頁面上被選中的文字的方法。最關鍵的JavaScriptAPI是：event.selection=window.getSelection();這里的selection實際上是個對象，但如果我們使用.toString()或強行轉化成字符串，我們將得到被選中的文字。$(document).ready(function(){$(".contenttext").mouseup(function(e){vartxt;</span> <p class="auth-span"> <span id="tjgufvlx2j" class="muted"><i class="fa fa-user"></i><span id="tjgufvlx2j" class="zj-icon-text">系統</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-clock-o"></i><span id="tjgufvlx2j" class="zj-icon-text">2019-08-29 23:32:32</span></span> <span id="tjgufvlx2j" class="muted"><i class="fa fa-eye"></i><span id="tjgufvlx2j" class="zj-icon-text">2656</span></span>  </p> </article><article class="excerpt"> <header> <a title="Javascript" class="label label-important zj-del-target" href="/category/66">Javascript<i class="label-arrow"></i></a> <h2> <a class="zj-titles zj-del-target" href="/article/17086" title="js javascript 文字變換顏色，樣式，改變文字的" target="_blank" onclick="return recordId('cid',66)">js javascript 文字變換顏色，樣式，改變文字的 </a> </h2> </header> <div id="tjgufvlx2j" class="focus"> <a class="zj-del-target" href="/article/17086" target="_blank"><img style="width: 200px; 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