var a;
var b;
for(var i=0;i<N1;i++){
a = A[i].split();
for(var j=0;j<N2;j++){
b = B[j].split();
if(a[0]==b[0]){
A[i] = B[j];
}
b = null;
}
a = null;
}
var b;
for(var i=0;i<N1;i++){
a = A[i].split();
for(var j=0;j<N2;j++){
b = B[j].split();
if(a[0]==b[0]){
A[i] = B[j];
}
b = null;
}
a = null;
}
<script language=javascript>
var a=new Array()
a[0]=new Array("111","aaa")
a[1]=new Array("222","bbb")
a[2]=new Array("333","ccc")
a[3]=new Array("444","ddd")
a[4]=new Array("555","eee")
var b=new Array()
b[0]=new Array("111","eee")
b[1]=new Array("222","fff")
b[2]=new Array("444","ggg")
//初始化结束
var temp=new Object();
for(var i=0;i<b.length;i++){
temp[b[i][0]]=b[i][1]
}
for(var i=0;i<a.length;i++)
{
if(temp[a[i][0]])
a[i][1]=temp[a[i][0]]
}
alert(a)
</script>