认识层次选择器

html页面：

<div   class="ex">
    <span>3</span>
    <span class="sp1">1</span>
    <span>22222222222</span>
    <span>3</span>
    <span>3</span>
    <span>3</span>
    <span>3</span>
    <div class="subEx">
        <span>4</span>
        <span>5</span>
    </div>
</div>

js代码：

<script>
    var num=$(".ex span").length;
    var num1=$(".ex>span").length;
    var txt1=$(".sp1+ span").text();
    var arr=$(".sp1~span")
    console.log(num);
    console.log(num1);
    console.log(txt1);
    console.log(arr.length);
</script>

结果显示：

最后的碎碎念

（1）$(".ex span")和$(".ex>span")的区别，$(".ex span")是选取.ex下的所有span元素，$(".ex>span")是选取.ex下的直接子元素
（2）$(".sp1+ span")和$(".sp1~span")的区别就是$(".sp1"）.next("span")和$(".sp1"）.nextAll("span")