如何设置元素，如果第一子女哈斯克斯

我有2个 .school，几个 .class-room，里面有一些 .my-child。

如果.my-child位于学校的第一个.class-room中，我想为具有黄色背景的学校设计。但这并不如预期的那样显示。

jsfiddle

$('.school').each(function() {
  $(this).find('.my-child').each(function(i, el) {
    $(this).addClass('child' + (i + 1));
  });
  if ($('.school .class-room:first-child').children().hasClass('.my-child')) {
    $('.school').css('background', 'yellow');
  }
})

.my-child.child1 {
  background: red;
}
.my-child.child2 {
  background: green;
}
.my-child.child3 {
  background: blue;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="school">
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
</div>
<br><br>
<div class="school">
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
</div>

您不能在Hasclass中使用点：

更改：

.hasClass('.my-child')

to：

.hasClass('my-child')

我还将在您的条件下使用$(this(，仅选择正确的学校来更改背景颜色：

if ( $(this).children('.class-room:first-child').children().hasClass('my-child') )

https://jsfiddle.net/5wxaoj1m/

编辑：已更新以解决评论中的问题，我添加了JSFiddle链接。

我建议移动each循环外选择的代码。然后，使用:has()选择器找到学校。

$('.school:has(.class-room:first-child>.my-child)').addClass('has-my-child');

.my-child.child1 {
  background: red;
}
.my-child.child2 {
  background: green;
}
.my-child.child3 {
  background: blue;
}
.has-my-child { background-color: yellow; }

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="school">
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
</div>
<br><br>
<div class="school">
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
</div>

请注意，这可能比使用普通旧JavaScript慢：

const school = Array.from(document.querySelectorAll('.school')).filter(school => school.querySelectorAll('.class-room:first-child > .my-child').length === 1)[0];
if (school) {
  school.classList.add('has-my-child');
}

.my-child.child1 {
  background: red;
}
.my-child.child2 {
  background: green;
}
.my-child.child3 {
  background: blue;
}
.has-my-child {
  background-color: yellow;
}

<div class="school">
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
</div>
<br><br>
<div class="school">
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
</div>

要获得预期的结果，请在以下选项中使用等式的索引和('：'：first-child'(

$(this).children('.class-room').eq(0).children('.my-child').is(':first-child')

1。首先带有等式(0(的班级
2.检查my-child是第一个或不使用儿童('。my-child'(。是('：'：first-child'(

$('.school').each(function() {
  $(this).find('.my-child').each(function(i, el) {
    $(this).addClass('child' + (i + 1));
  });
  
  if($(this).children('.class-room').eq(0).children('.my-child').is(':first-child')){
    $(this).css('background', 'yellow')
  }
  
})

.my-child.child1 {
  background: red;
}
.my-child.child2 {
  background: green;
}
.my-child.child3 {
  background: blue;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="school">
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
</div>
<br><br>
<div class="school">
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
  <div class="class-room">
    <div class="my-child">Child</div>
  </div>
  <div class="class-room">
    <div class="other">Child</div>
  </div>
</div>

codepen -https：//codepen.io/nagasai/pen/mybbej

我相信您可以摆脱javaScript并在CSS上做到这一点。

将其添加到您的CSS：

.class-room:first-of-type > .my-child { background: yellow; }

应该照顾的。

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