js 去重

1.方法一：

 function removeDuplicatedItem1(ar){
        var ret =[];
        for(var i = 0,j = ar.length ;i<j;i++){
            if(ret.indexOf(ar[i]) === -1){
                ret.push(ar[i]);
            }
        }
        document.write(ret);
    }

var arr = [1,2,3,2,32,34,2,3,4,3,4,24,2,42,42,42,43,43,34,4,3];
removeDuplicatedItem1(arr)

2.方法二：

function removeDuplicatedItem2(ar){
        var tmp = {},ret = [];
        for(var i = 0,j=ar.length;i<j;i++){
            if(!tmp[ar[i]]){
                tmp[ar[i]] = 1;
                ret.push(ar[i]);
            }
        }
        document.write(ret);
    }
var arr = [1,2,3,2,32,34,2,3,4,3,4,24,2,42,42,42,43,43,34,4,3];
removeDuplicatedItem2(arr);

3.方法三：

function  removeDuplicatedItem3(ar){
    var ret = [];
    ar.forEach(function(e,i,ar){
        if(ar.indexOf(e) === i){
            ret.push(e);
        }
    });
    document.write(ret);
}
var arr = [1,2,3,2,32,34,2,3,4,3,4,24,2,42,42,42,43,43,34,4,3];
removeDuplicatedItem3(arr);

4.方法四：

function  removeDuplicatedItem4(ar){
    var ret = [],end;
    ar.sort();//当做字符串进行排序，如果大小排序还要重新调用别的方法；
    end = ar[0];
    ret.push(ar[0]);
    for(var i = 1;i<ar.length;i++){
        if(ar[i] != end){
            ret.push(ar[i]);
            end = ar[i];
        }
    }
    document.write(ret);
}
var arr = [1,2,3,2,32,34,2,3,4,3,4,24,2,42,42,42,43,43,34,4,3];
removeDuplicatedItem4(arr);