数组的合并，去重，排序

var arr1 = [‘a‘,‘b‘];
var arr2 = [‘a‘,‘c‘,‘d‘];
var arr3 = [1,‘d‘,undefined,true,null];

//合并两个数组，去重
var concat_ = function(arr1,arr2){
    //不要直接使用var arr = arr1，这样arr只是arr1的一个引用，两者的修改会互相影响
    var arr = arr1.concat();
    //或者使用slice()复制，var arr = arr1.slice(0)
    for(var i=0;i<arr2.length;i++){
        arr.indexOf(arr2[i]) === -1 ? arr.push(arr2[i]) : 0;
    }
    return arr;
}
console.log(concat_(arr1,arr2));   //[‘a‘,‘b‘,‘c‘,‘d‘]

var arr1 = [‘a‘,‘b‘];
var arr2 = [‘a‘,‘c‘,‘d‘];
var arr3 = [1,‘d‘,undefined,true,null];
//合并多个数组，去重
var concat_ = function(arr1,arr2,arr3){
    if(arguments.length <= 1){
        return false;
    }
    var concat_ = function(arr1,arr2){
        var arr = arr1.concat();
        for(var i=0;i<arr2.length;i++){
            arr.indexOf(arr2[i]) === -1 ? arr.push(arr2[i]) : 0;
        }
        return arr;
    }
    var result = concat_(arr1,arr2);
    for(var i=2;i<arguments.length;i++){
        result = concat_(result,arguments[i]);
    }
    return result;
}
console.log(concat_(arr1,arr2,arr3));//["a", "b", "c", "d", 1, undefined, true, null]

//合并多个数组，去重，排序
var arr1 = [1,6,4,0];
var arr2 = [8,20,7,4.5];
var arr3 = [6,0,7,90,2];

var concat_ = function(arr1,arr2,arr3){
    if(arguments.length <= 1){
        return false;
    }
    var concat_ = function(arr1,arr2){
        var arr = arr1.concat();
        for(var i=0;i<arr2.length;i++){
            arr.indexOf(arr2[i]) === -1 ? arr.push(arr2[i]) : 0;
        }
        return arr;
    }
    var result = concat_(arr1,arr2);
    for(var i=2;i<arguments.length;i++){
        result = concat_(result,arguments[i]);
    }
    //排序
    function sortNumber(a,b){
        return a - b;
    }
    return result.sort(sortNumber);
}
console.log(concat_(arr1,arr2,arr3))//[0, 1, 2, 4, 4.5, 6, 7, 8, 20, 90]