第一种

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title>
</head>
<body><script>var str='';var num=prompt("请输入几行几列")for(var i=1;i<=num;i++){for(var j=1;j<=i;j++){str+=j+"*"+i+"="+i*j+"\t";}str+="\n";}alert(str);console.log(str);</script>
</body>
</html>
第二种

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>for语句</title><style>td{border: 1px solid black;}</style><script>document.write("<table align='center'>");for(var i=1;i<=9;i++){document.write("<tr>");for (var j=1;j<=i;j++){document.write("<td>");document.write(i +" * "+ j + " = "+ (i * j )+" ");document.write("</td>");}document.write("</tr>");}document.write("</table>");</script>
</head>
<body>
</body>
</html>