for循环，颜色由奇偶判断，

img

参考这个


<!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>
    <style>
        .red{
            color: red;
        }
      
    </style>
</head>

<body>
    <div id="box">

    </div>
</body>
<script>
    let box = document.getElementById("box");
    let a = ""
    for (var i = 1; i < 8; i++) {
        for (var j = 1; j < 8; j++) {
            if (j % 2 == 0) {
                a += `
             <span class="bl">6</span>
            `
            } else {
                a += `
             <span class="red">7</span>
            `
            }
        }
        a+="<br/>"
    }

    box.innerHTML = a;



</script>

</html>

if(j%2==0) //偶数列（0,2,4列）
if(j%2==1) //奇数列（1,3,5列）

用索引去判断

用 CSS控制不行吗？使用nth(even|odd),下列给出的代码“table tr:”用合适的标签替代。

<style type="text/css">
table tr:nth-child(odd) {
  background-color:#F5F5F5;
}
table tr:nth-child(even) {
  background-color:#fff;
}
</style>