IE下JavaScript数组问题

Question

我有段JavaScript代码如下:var DATA = [
  ["00002","9900","","","2009-11-23 17:51:52","0001","0002","+1.5","","","","","","",""],
  ["00003","9900","","","2009-11-23 17:52:15","0001","0002","-1","","","","","","","0"],
  ["00004","9900","","","2009-11-23 17:53:02","0001","0002","-1","","","","","","","0"],
  ["00005","9900","","","2009-11-23 17:52:52","0001","0002","-1","","","","","","","0"],
  ["00006","9900","","","2009-11-23 17:52:52","0001","0002","-1","","","","","","","0"],
  ["00007","9900","","","2009-11-23 17:52:52","0001","0002","-1","","","","","","","0"],
  ["00008","9900","","","2009-11-23 17:52:52","0001","0002","-1","","","","","","","0"],
  //...后面还有很多，一共有5000多条
];
var strB = '';
function test(){
for(var i=0,len=DATA.length;i<len;i++) {
strB += '\r\n';
}
}
var t1=Date.parse(new Date()) + new Date().getMilliseconds();
test();
var t2=Date.parse(new Date()) + new Date().getMilliseconds();
alert(t2-t1);这样一段函数在IE下的执行下要几秒钟，而FF、Chrome下只要几毫秒
如果我把上面那个数组给注释掉，再在IE下执行，也只需要几毫秒难道前面的大数组会影响后面的函数的执行？？我函数里根本就没有用到这个大数组啊请高手告诉一下原因，以及在IE下如何改进

Answer 1

CPU P4 2.66G 需要6秒左右

Answer 2

当然会用了，不过不在那个test里用

Answer 3

本来IE这方面就没有FF做的好，如果量再大点，弄个2万条，可能会内存报错，你试试？

Answer 4

你拿这个数组的长度进行循环了，还说没用到数据量大的时候不要用字符串拼接的方式，用数组代替，可以这样：
var strB = []; 
function test(){ 
var len=DATA.length;
var i=0;
for(;i <len;i++) { 
strB[strB.length] = '\r\n'; 
} 
} 
var t1=Date.parse(new Date()) + new Date().getMilliseconds(); 
test(); 
var t2=Date.parse(new Date()) + new Date().getMilliseconds(); 
alert(t2-t1);
alert(strB.length);//数组长度
strB.join("");//转字符串

Answer 5

大数组会影响后面的函数执行时间,以下可以尝试看看.........
修改方案：var strB = new Array();
function test(){
    var dataLen = DATA.length;
    for(var i = 0,i < dataLen; i++) { 
        strB.push("\r\n");
    } 
}

Answer 6

已经测试过了，时间都浪费在字符串拼接上！！！改成 Array 能提高两个数量级，可是还没有 ff 快，
可见 IE 的大字符串拼接存在严重的效率问题！L@_@K
var strB = new Array();
function test(){
for(var i=0,len=DATA.length; i<len; i++) {
strB.push("\r\n");
}
}

Answer 7

长度影响循环次数，循环次数影响执行时间LZ可以把DATA.length直接换成5000，把数组去掉看看，还是一样的慢

Answer 8

如果把数组去掉，DATA.length改成5000，只需要几毫秒

Answer 9

for(;i <len;i++) {
   //直接用i，不是更省事
   strB[i] = '\r\n';
}
}

Answer 10

其实 lz 只要分段计时就能知道时间到底消耗在哪里了！IE 解释数组只用几毫秒，时间主要消耗在【字符串拼接】上，
记得 IE 会把字符串作为字符数组处理，即 CharArray，每次拼接后产生一个新的 String 实例。

Answer 11

经过测试，这个地方主要是由于DATA数组占用大量的内存导致,可以在获取完数组长度后释放内存：
var len=DATA.length;
DATA = null;
for(var i=0;i <len;i++) { 
strB += '\r\n'; 
}当然最好还是不要使用字符串拼接的方式