均打印在浏览器的控制台

直角在右下的三角形

<script>
        //右下角三角形
        var alt = "";
        for(var i=1; i<=7; i++){
            var blank = "";
            for(var j=1; j<=7-i; j++){   //打印空格
                blank += " ";
            }
            var stars = "";
            for(var m=1; m<=i; m++){    //打印*
                stars += "*";
            }
            alt += blank + stars + "\n";   //字符串的拼接,拼为一行
        }
        console.log(alt);
    </script>

等腰三角形

    <script>
        //等腰三角形
        var alt = "";
        for(var i=1; i<=5; i++){
            var blank = "";
            for(var j=1; j<=5-i; j++){   //打印空格
                blank += " ";
            }
            var stars = "";
            for(var m=1; m<=2*i-1; m++){    //打印*
                stars += "*";
            }
            alt += blank + stars + "\n";   //字符串的拼接,拼为一行
        }
        console.log(alt);
    </script>

菱形

<script>
        //菱形
            var alt = "";
            var _num = 5;
            for(var i=1; i<=_num; i++){
                var blank = "";
                for(var j=1; j<=_num-i; j++){   //打印空格
                    blank += " ";
                }
                var stars = "";
                for(var m=1; m<=2*i-1; m++){    //打印*
                    stars += "*";
                }
                alt += blank + stars + "\n";   //字符串的拼接,拼为一行
            }
            for(var i=_num-1; i>0; i--){    //打印的行数要减1
                var blank = "";
                for(var j=1; j<=_num-i; j++){   //打印空格
                    blank += " ";
                }
                var stars = "";
                for(var m=1; m<=2*i-1; m++){    //打印*
                    stars += "*";
                }
                alt += blank + stars + "\n";   //字符串的拼接,拼为一行
            }
            console.log(alt);
    </script>