JSS作业：

1:

<script>
    var cnt = parseInt(window.prompt("请输入打印的行数："));
    for (var i = 1; i <= cnt; i++){
        for (var j = 1; j <= i; j++){
            document.write("*")
        }
        document.write("<br>")
    }
</script>

2:

<script>
    let cnt = parseInt(prompt("请输入要打印的行数："));
    for(var i=1;i<=cnt;i++){
        for(var j=1;j<=cnt-i;j++){
            document.write("&nbsp;");
        }
        for(var j=1;j<=2*i-1;j++){
            document.write("*");
        }
        document.write("<br/>");
         }
</script>

3:

<script>
    let cnt = parseInt(prompt("请输入要打印的行数："));
    for(var i=0; i<cnt; i++){       
        for(var j=cnt; j>i; j--){
            document.write("&nbsp");
        }      
        for(var k=0;k<2*i+1;k++){
            document.write("*");
        }      
        document.write("</br>");
    }
    for(var i=cnt-1; i>0; i--){
        
        for(var j=cnt; j>=i; j--){
            document.write("&nbsp");
        }   
        for(var k=0; k<2*i-1; k++){
            document.write("*");
        }
        document.write("</br>")
    }
</script>

4:

<script>
    var num=0;
    for(var i=1; i<10; i++){
        for(var j=1; j<10; j++){
            num = i * j;
            if(num / 10 < 1){
                num="&nbsp;&nbsp;" + i * j;
            }
            if(j<=i) {
                document.write(j + "*" + i + "=" + num + "&nbsp;&nbsp;&nbsp;&nbsp;");
            }
        }   
        document.write("<br>");
    }
</script>