原生js

var arr1 = [1, 1, '1', '1'];
    function unique(arr) {
        // res用来存储结果
        var res = [];
        for (var i = 0, Len = arr.length; i < Len; i++) {
            for (var j = 0, resLen = res.length; j < resLen; j++ ) {
                if (arr[i] === res[j]) {
                    break;
                }
            }
            // 如果array[i]是唯一的，那么执行完循环，j等于resLen
            if (j === resLen) {
                res.push(arr[i])
            }
        }
        return res;
    }
    console.log(unique(arr1)); // [1, "1"]

利用indexOf

    function unique(arr) {
        let  res = [];
        for (let  i = 0, len = arr.length; i < len; i++) {
            var current = arr[i];
            if (res.indexOf(current) ===-1)){
                res.push(current);
            }
        }
        return res;
    }
    console.log(unique(arr1));

利用filter()方法

    var arr2= [1, 2, 1, 1, '1'];
    function unique(arr) {
        var res = arr.filter(function(item, index, array){
            return array.indexOf(item) === index;
        })
        return res;
    }
    console.log(unique(arr2));

ES6

    var arr = [1,3,1,4,1,5,6,3,1,2];
    Array.from(new Set(arr));//[1, 3, 4, 5, 6, 2]

[... new Set(arr)];//[1, 3, 4, 5, 6, 2]