JS在合并多个数组时如何去重

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));

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));

//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));