求大神指导一个JS问题

Question

var arr2 = ["WEST","NORTH"];
var num1 = 0;
function checkDir(arr,num){
        if (num == arr.length-1 || arr == '' || arr == ["NORTH","WEST","SOUTH","EAST"]) {
            alert(arr);
            return arr;
        }else{
            alert("走了这里");
        switch(arr[num]){
            case "NORTH":
            alert(1);
            dirCompare("SOUTH",num,arr);
            break;
            case "SOUTH":
            alert(2);
            dirCompare("NORTH",num,arr);
            break;
            case "EAST":
            alert(3);
            dirCompare("WEST",num,arr);
            break;
            case "WEST":
            alert(4);
            dirCompare("EAST",num,arr);
            break;
        }
    }
}


function dirCompare(str,num,arr1){
    var switch1 = 0;
    for (var i = num+1; i < arr1.length; i++) {
        if (arr1[i]==str){
            arr1.splice(num,1);
            arr1.splice(i-1,1);
            switch1 = 1;
            checkDir(arr1,num);
            return;
        }
    };
    if (switch1 == 0){
        num++;
        alert(arr1 + "-" + num);
        checkDir(arr1,num);
    }
} 
alert(checkDir(arr2,num1));

这是一个判断方向的需求，每一对东西或南北都被剔除，上面函数里直接判断无法消除的两个方向，一直到第一个if条件中的alert都能正确返回需要的结果，但是后面的return arr似乎就没有被执行，最后函数返回值也是undefined，求大神解惑这是哪地方写错了。

Answer 1

     var arr2 = ["WEST", "NORTH"];
    var num1 = 0;
    function checkDir(arr, num) {
        if (num == arr.length - 1 || arr == '' || arr.join() == ["NORTH", "WEST", "SOUTH", "EAST"]) {
            alert(arr);
            alert('return')
            return arr;
        } else {
            alert("走了这里");
            switch (arr[num]) {
                case "NORTH":
                    alert(1);
                   return dirCompare("SOUTH", num, arr);/////////要return返回值
                    break;
                case "SOUTH":
                    alert(2);
                    return dirCompare("NORTH", num, arr);/////////要return返回值
                    break;
                case "EAST":
                    alert(3);
                    return dirCompare("WEST", num, arr);/////////要return返回值
                    break;
                case "WEST":
                    alert(4);
                    return dirCompare("EAST", num, arr);/////////要return返回值
                    break;
            }
        }
    }


    function dirCompare(str, num, arr1) {
        var switch1 = 0;
        for (var i = num + 1; i < arr1.length; i++) {
            if (arr1[i] == str) {
                arr1.splice(num, 1);
                arr1.splice(i - 1, 1);
                switch1 = 1;
                return checkDir(arr1, num);/////////要return返回值
                //return;
            }
        };
        if (switch1 == 0) {
            num++;
            alert(arr1 + "-" + num);
            return checkDir(arr1, num);/////////要return返回值
        }
    }
    alert(checkDir(arr2, num1));

除非第一次执行checkDir成功才会执行return，else分支你的其他函数要增加return