数组去重和查找出现最多的字符（HTML5）+几个小题

1.去除重复的数据

<script>
//数组去重
var a=["a","b","c","a","d","e","f","a","s","c"];
var b=[];
var p=0;
for(var i=0; i<a.length;i++){
var value=a[i];
if(b.indexOf(value)==-1){
b[p++]=value;
}

}
console.log(b);
</script>

2.出现次数统计

3.判断IP是否合理

4.判断手机号码书否合理