js 可以帮我详细解答一下每行的意思和原理吗，谢谢

Question

 for (var i = 0; i < l; i++) { 
      for (var j = 0; j < (l - i - 1); j++)
          document.write('&nbsp;');
      var a = 2 * i + 1; //星星个数
      for (var k = 4; k < a; k++) {
          document.write(k == i ? "☆" : "★");
      }
          document.write('</br>');
      }

Answer 1

输出三角形的星星

 var l =9;
    for (var i = 0; i < l; i++) {
        for (var j = 0; j < (l - i - 1); j++) {
            document.write('。');
        }
        var a = 2 * i + 1; //星星个数
        for (var k = 4; k < a; k++) { //从第k+1行开始，显示☆
            document.write(k == i ? "☆" : "★");
        }
        document.write('</br>');
    }