JavaScript代码优化实战之一：缓存变量，关键字过滤

　　无意中看到某网站的一段JS代码：

function clearSearchText(){
var searchtext = document.getElementById("searchwordl").value
document.getElementById("searchwordl").value="";
}
function replaceALL(){
var replaceTxt = document.getElementById("searchwordl").value;
var relTxt = replaceTxt.replace(/^\s+|\s+$/g,"");
if(typeof(document.getElementById("searchwordl"))=="undefined"||relTxt==""){
alert("请输入检索条件");
document.getElementById("searchwordl").focus();
return false;
}
if(typeof(document.getElementById("searchwordl"))!="undefined"){
var searchwordl = document.getElementById('searchwordl').value;

var sig = 0;
if(searchwordl.indexOf("'") > -1 || searchwordl.indexOf("\"") > -1 || searchwordl.indexOf("%") > -1 || searchwordl.indexOf("#") > -1 || searchwordl.indexOf("&") > -1 || searchwordl.indexOf("*") > -1 || searchwordl.indexOf("(") > -1 || searchwordl.indexOf(")") > -1 || searchwordl.indexOf("@") > -1 || searchwordl.indexOf("`") > -1 || searchwordl.indexOf("/") > -1 || searchwordl.indexOf("\\") > -1 || searchwordl.indexOf(",") > -1 || searchwordl.indexOf(".") > -1 || searchwordl.indexOf("=") > -1 || searchwordl.indexOf("<") > -1 || searchwordl.indexOf(">") > -1)
sig = 1;

searchwordl=searchwordl.replace("'","");
//searchwordl=searchwordl.replace(" ","");
searchwordl=searchwordl.replace("%","");
searchwordl=searchwordl.replace("#","");
searchwordl=searchwordl.replace("&","");
searchwordl=searchwordl.replace("*","");
searchwordl=searchwordl.replace("(","");
searchwordl=searchwordl.replace(")","");
searchwordl=searchwordl.replace("@","");
searchwordl=searchwordl.replace("`","");
searchwordl=searchwordl.replace("/","");
searchwordl=searchwordl.replace("\\","");
searchwordl=searchwordl.replace(",","");
searchwordl=searchwordl.replace(".","");
searchwordl=searchwordl.replace("=","");
searchwordl=searchwordl.replace("<","");
searchwordl=searchwordl.replace(">","");
if(searchwordl == '请输入搜索条件'){
alert("请输入搜索条件");
return false;
}
if(searchwordl == ''){
alert("请正确输入搜索条件");
return false;
}
if(sig == 1){
alert("请正确输入搜索条件");
return false;
}
document.getElementById('searchword').value=searchwordl;
return true;
//document.fmsearch.submit();
}
}

　　场景是网页上有一个搜索框，输入框的onfocus事件调用了clearSearchText方法，提交前调用了replaceALL方法。

　　以上代码主要存在以下问题：

　　1、逻辑不对：onfocus事件直接把内容清空是不合理的。

　　2、常用到的变量没有缓存：多次用到了document.getElementById("searchwordl")

　　3、变量没有集中声明

　　4、JavaScript中的replace方法只替换一次，上面的代码中原意应该是全部替换

　　5、代码臃肿

　　由于最近正在看JavaScript代码优化方面的书，所以一时手痒就对这段代码进行了一个优化，现在分享出来，欢迎大家点评。

function clearSearchText(){
var search=document.getElementById("searchwordl");
search.value= search.value == search.defaultValue ? "":search.value;
}

function replaceALL(){
var search=document.getElementById("searchwordl"),
searchword = search.value.replace(/ /g,"");
if(searchword == ""){
alert("请输入检索条件");
search.focus();
return false;
}
searchword=searchword.replace(/['%#&\*\(\)@`\/\\,\.=<>]/g,"");
if(searchword == search.defaultValue || searchword == ''){
alert("请正确输入搜索条件");
search.focus();
return false;
}
search.value=searchword;
return true;
}

　　另外，页面中用了jQuery，所以上面的代码如果用jQuery会更简洁。

　　欢迎大家给出更好的优化方案。