javascript - 如何优化这个 JSP/JavaScript 代码？

Question

我有一个jsp，它使用了大量的javascript，但速度不够快。我想首先对其进行优化，这是代码的一部分:

在jsp中我进行了初始化:

window.onload = function () {
        formCollection.pageSize.value = "<%= pagingSize%>";
        elemCollection = iDom3.Table.all["spis"].XML.DOM;
        <%  if (resultList != null) { %>
        elementsNumber = <%= resultList.size() %>;
        <%} else { %>
        elementsNumber = 0;
        <% } %> 
        contextPath = "<%= request.getContextPath() %>";
    }

在我的 js 文件中，我有两种类型的 js 函数:

// gets the first element and sets it's value to all the other; 
//the selectSingleNode function is used because I use XSLT transformation 
//to generate the table

_setTehJed = function(){    
        var resultId = formCollection.elements["idTehJedinice_spis_1"].value;
        var resultText = formCollection.elements["tehnicka_spis_1"].value;
        if (resultId != ""){
            var counter = 1;
            while (counter<elementsNumber){
                counter++;
                if(formCollection.elements["idTehJedinice_spis_"+counter] != null){
                    formCollection.elements["idTehJedinice_spis_"+counter].value=resultId;
                    formCollection.elements["tehnicka_spis_"+counter].value=resultText;
                }
                var node=elemCollection.selectSingleNode("/suite/table/rows/row[@id = 'spis_"+counter+"']/data[@col = 'tehnicka']/title");
                node.text=resultText;
                var node2=elemCollection.selectSingleNode("/suite/table/rows/row[@id = 'spis_"+counter+"']/data[@col = 'idTehJedinice']/title");
                node2.text=resultId;
            }
        }

    }

// sets the elements checkbox to checked or unchecked
_SelectCheckRokCuvanja = {
        all : [],

        Item : function (oItem, sId) {
                this.all["spis_"+sId] = oItem.value;
                if (oItem.checked) {
                    elemCollection.selectSingleNode("/suite/table/rows/row[@id = 'spis_"+sId+"']/data[@col = 'rokCheck']").setAttribute("default", "true");
                }else{
                    elemCollection.selectSingleNode("/suite/table/rows/row[@id = 'spis_"+sId+"']/data[@col = 'rokCheck']").setAttribute("default", "false");
                }
        }
    }

我使用了这些技巧:

• https://web.archive.org/web/20151029015752/http://blogs.msdn.com:80/b/ie/archive/2006/08/28/728654.aspx
• http://code.google.com/speed/articles/optimizing-javascript.html

但我仍然认为可以做一些事情，比如定义这样的函数:

在jsp中:

window.onload = function () {
        iDom3.DigitalnaArhivaPrihvat.formCollection=document.forms["controller"];
        iDom3.DigitalnaArhivaPrihvat.formCollection.pageSize.value = "<%= pagingSize%>";
        iDom3.DigitalnaArhivaPrihvat.elemCollection = iDom3.Table.all["spis"].XML.DOM;
        <%  if (resultList != null) { %>
        iDom3.DigitalnaArhivaPrihvat.elementsNumber = <%= resultList.size() %>
        <%} else { %>
        iDom3.DigitalnaArhivaPrihvat.elementsNumber = 0;
        <% } %> 
}

在js中:

iDom3.DigitalnaArhivaPrihvat = {
        
    formCollection:null,
    elemCollection:null,
    elementsNumber:null,


_setTehJed : function(){    
        var resultId = this.formCollection.elements.idTehJedinice_spis_1.value;
        var resultText = this.formCollection.elements.tehnicka_spis_1.value;
        if (resultId != ""){
            var counter = 1;
            while (counter<this.elementsNumber){
                counter++;
                if(this.formCollection.elements["idTehJedinice_spis_"+counter] !== null){
                    this.formCollection.elements["idTehJedinice_spis_"+counter].value=resultId;
                    this.formCollection.elements["tehnicka_spis_"+counter].value=resultText;
                }
                var node=this.elemCollection.selectSingleNode("/suite/table/rows/row[@id = 'spis_"+counter+"']/data[@col = 'tehnicka']/title");
                node.text=resultText;
                var node2=this.elemCollection.selectSingleNode("/suite/table/rows/row[@id = 'spis_"+counter+"']/data[@col = 'idTehJedinice']/title");
                node2.text=resultId;
            }
        }

    },

_SelectCheckRokCuvanja = {
        all : [],

        Item : function (oItem, sId) {
                this.all["spis_"+sId] = oItem.value;
                if (oItem.checked) {
                    this.elemCollection.selectSingleNode("/suite/table/rows/row[@id = 'spis_"+sId+"']/data[@col = 'rokCheck']").setAttribute("default", "true");
                }else{
                    this.elemCollection.selectSingleNode("/suite/table/rows/row[@id = 'spis_"+sId+"']/data[@col = 'rokCheck']").setAttribute("default", "false");
                }
        }
    }

但问题在于范围界定(如果我这样做，第二个函数将无法正确执行)。有什么建议吗？

编辑:表的数据结构:

<row id="spis_3">
    <data col="rokCheck" type="check" default="false" onchange="_ChangeTypeRokCuvanje(this,'3')" >
    <title>false</title>
    <description>Tehnička jedinica</description>
</data>

Answer 1

selectSingleNode() 是一个相当昂贵的操作。你应该尽量避免它。解决办法有两种:

1. 自己迭代数据结构(这样您就不必在 DOM 中搜索表，而是可以直接逐行修改)。

2. 由于您为每一行分配一个 ID，因此您应该能够使用 document.getElementById()，而无需昂贵的 XPath 查找。

3. 使用 jquery 之类的框架一次获取所有相关节点(-> 仅 1 次昂贵的查找)，然后迭代列表。

[编辑]参见Traversing an HTML table with JavaScript and DOM Interfaces有关如何实现 #1 的示例。