javascript如何操作数组

var arr1=[1,2,3,4,5,6,7];
var arr2=[];
var arr3=[1,2,3,4,5,6,7,8,9,10];
function filterData(arr){
    var maxLength=10;
    var minLength=arr.length;
    var bottom=[];
    var defaultArr=[];
    var defaultLength=maxLength-minLength;
    if(defaultLength!=0){
        for(var i=0;i<defaultLength;i++){
            defaultArr.push(‘a‘);
        }
        arr=arr.concat(defaultArr);
    }
    for(var j=0;j<minLength;j++){
        bottom.push(arr[j]);
    }

    console.log(arr,bottom);
};
filterData(arr1);//[1, 2, 3, 4, 5, 6, 7, "a", "a", "a"], [1, 2, 3, 4, 5, 6, 7]
filterData(arr2);//["a", "a", "a", "a", "a", "a", "a", "a", "a", "a"] []
filterData(arr3);//[1, 2, 3, 4, 5, 6, 7, 8, 9, 10] , [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]