var arr1=[1,2,3];
var arr2=['a','b'];
var arr3=[null,undefined];
var arr = arr1.concat(arr2,arr3);   //合併一
var arr4=[['c','d'],3];
arr=arr1.concat(arr4)
//concat函式，可以合併多個數組，不影響原陣列，但會造成記憶體浪費，不能處理巢狀陣列

function marry_for(arr1,arr2) {
    if(arr1.length > arr2.length){
        for(var i=0;i<arr2.length;i++){
            arr1.push(arr2[i]);
        }
        return arr1;
    }else{
        for(var i=0;i<arr1.length;i++){
            arr2.push(arr1[i]);
        }
        return arr2;
    }
}
arr1 = [1,2,3,4] ;arr2 = [5,[6,7,8],9,10] ;
console.log(marry_for(arr1, arr2));
 

function  marry_foreach(arr1,arr2) {
    if(arr1.length > arr2.length){
        arr2.forEach(function (value,index,arr2) {
            arr1.push(value);
        })
        return arr1;
    }
    else{
        arr1.forEach(function (value,index,arr1) {
            arr2.push(value);
        })
     return arr2;
    }
}
arr1 = [1,2,3,4] ;arr2 = [5,[6,7,8],9,10];
console.log(marry_foreach(arr1,arr2));
 

function marry_reduce(arr1,arr2) {
    if(arr1.length>arr2.length){
        return arr2.reduce(function (prev, second) {    //升序新增
            prev.push(second);
            return prev;
        },arr1)
    }
    else{
        return arr1.reduceRight(function (prev,second) {  //降序新增
        prev.push(second);
        return prev;
        },arr2)
    }
}
arr1 = [1,2,3,4] ;arr2 = [5,[6,7,8],9,10] ;
console.log(marry_reduce(arr1,arr2)
 

function marry_apply(arr1,arr2){
    return Array.prototype.concat.apply([],arguments)
}
arr1 = [1,2,3,4] ;arr2 = [5,[6,7,8],9,10] ;
console.log(marry_apply(arr1,arr2))