JavaScript: 通过循环按行顺序为一个5x5的二维数组a赋1到25的自然数,然后输出该数组的左下半三角。试编程

        var arr = [
            [1, 2, 3, 4, 5],
            [6, 7, 8, 9, 10],
            [11, 12, 13, 14, 15],
            [16, 17, 18, 19, 20],
            [21, 22, 23, 24, 25]
       ];

       for(var i = 0; i< arr.length; i++) {
           for(var j = 0; j<=i; j++) {
               document.write(arr[i][j] + "&nbsp");
           }
           document.write("<br/>");
       }