jQuery查找前提？

当我想要找到一个对象的孩子时,我可以使用children();当我想在另一个对象中找到一个对象时,不一定是小孩,可以使用find().如果我想找一个父母,我使用parent(),但是如果我想找到一个先行者,不知道是否是父母祖父母,祖父母,我该怎么办？

我会给你一个例子：我正在构建一个应用于一些“输入：文本”的插件.

最后,我需要做一些事情来保持他们的形式.但有时,文本框将直接在表单中,或者它们可以在无序列表或表内.

我能否以一般的方式参考表格？

解决方法

您可以使用jQuery的最近()方法：

$('input:text').change(
function(){
    var ancestorFormElement = $(this).closest('form');
    // do stuff.
});

$('input:text').change(function() {
  var ancestorFormElement = $(this).closest('form');
 
  ancestorFormElement.addClass('hasInputChanged');
});

form {
  border: 2px solid #000;
  padding: 1em;
}
form.hasInputChanged {
  border-color: limegreen;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<form action="#" method="post">
  <fieldset>
    <legend>Simple demo</legend>
    <label for="name">Text Input:</label>
    <input type="text" name="name" id="name" value="" tabindex="1" />
  </fieldset>
</form>

外部JS Fiddle demo,用于实验或开发.

或者,您可以简单地使用将< form>元素与其后代的形式元素(< input>,< textarea>,< select>等)：

$('input:text').change(function() {
  var ancestorFormElement = this.form;
 
  // because 'this.form' returns a DOM node,it
  // must be converted to a jQuery object in 
  // order to utilise jQuery methods:
  $(ancestorFormElement).addClass('hasInputChanged');
});

$('input:text').change(function() {
  var ancestorFormElement = this.form;
 
  $(ancestorFormElement).addClass('hasInputChanged');
});

form {
  border: 2px solid #000;
  padding: 1em;
}
form.hasInputChanged {
  border-color: limegreen;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<form action="#" method="post">
  <fieldset>
    <legend>Simple demo</legend>
    <label for="name">Text Input:</label>
    <input type="text" name="name" id="name" value="" tabindex="1" />
  </fieldset>
</form>

外部JS Fiddle demo,用于实验或开发.

此外,因为我强烈怀疑你想要改变 – 无论如何 – 要恢复“改变”,我建议采取以下方法：

$('input:text').change(function() {
  var ancestorFormElement = this.form;
 
  // here we use the 'toggleClass(<class-name>,<switch>)'
  // method; where the 'switch' returns a Boolean true/false
  // if it evaluates to true then the class-name is added
  // and if it evaluates to false then the class-name is
  // removed:
  $(ancestorFormElement).toggleClass('hasInputChanged',this.value !== this.defaultValue);
});

$('input:text').change(function() {
  var ancestorFormElement = this.form;
 
  $(ancestorFormElement).toggleClass('hasInputChanged',this.value !== this.defaultValue);
});

form {
  border: 2px solid #000;
  padding: 1em;
}
form.hasInputChanged {
  border-color: limegreen;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<form action="#" method="post">
  <fieldset>
    <legend>Simple demo</legend>
    <label for="name">Text Input:</label>
    <input type="text" name="name" id="name" value="" tabindex="1" />
  </fieldset>
</form>

外部JS Fiddle demo,完全可以将更改事件处理程序委派给< form>元素本身,使用on()：

$('form').on('change',function(e) {
 
  // here 'e' is the event-object passed to the
  // event-handling function; 'e.target' is the
  // element that received the initiating event:
  var changedEl = e.target;
 
  $(this).toggleClass('hasInputChanged',changedEl.value !== changedEl.defaultValue);
});

$('form').on('change',function(e) {
  var changedEl = e.target;
 
  $(this).toggleClass('hasInputChanged',changedEl.value !== changedEl.defaultValue);
});

form {
  border: 2px solid #000;
  padding: 1em;
}
form.hasInputChanged {
  border-color: limegreen;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<form action="#" method="post">
  <fieldset>
    <legend>Simple demo</legend>
    <label for="name">Text Input:</label>
    <input type="text" name="name" id="name" value="" tabindex="1" />
  </fieldset>
</form>

外部JS Fiddle demo,用于实验或开发.

也可以将选择器传递给on()方法来指定应该启动给定事件的元素(这里是“change”事件)到
触发与祖先绑定的事件处理：

// here we pass the selector,'input[type=text]' to the
// method,which restricts the event-handling to only
// those events originating with <input> elements whose
// 'type' attribute is equal to 'text':
$('form').on('change','input[type=text]',function(e) {
 
  $(this).toggleClass('hasInputChanged',function(e) {
  var ancestorFormElement = this.form;
 
  $(ancestorFormElement).toggleClass('hasInputChanged',this.value !== this.defaultValue);
});

form {
  border: 2px solid #000;
  padding: 1em;
}
form.hasInputChanged {
  border-color: limegreen;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<form action="#" method="post">
  <fieldset>
    <legend>Simple demo</legend>
    <label for="name">Text Input:</label>
    <input type="text" name="name" id="name" value="" tabindex="1" />
  </fieldset>
</form>

外部JS Fiddle demo,用于实验或开发.

最后,一个纯粹的JavaScript手段完成了同样的行为：

// defining a named function to handle the
// event-handling,the 'event' argument is
// passed automagically from the
// addEventListener() method (below):
function changeHandler(event) {
 
  // 'this' is the element to which
  // event-handler was bound (again
  // automagically passed from
  // addEventListener()):
  var form = this,changed = event.target;
 
  // here we use the Element.classList API; which
  // works much as toggleClass() does,adding the
  // supplied class-name if the switch that follows
  // evaluates to true,removes it if the switch
  // evaluates to false:
  form.classList.toggle('hasInputChanged',changed.value !== changed.defaultValue);
 
}
 
// retrieving the <form> element using
// document.querySelector(),which returns
// the first element in the document that
// matches the CSS selector passed to the
// function:
var formElement = document.querySelector('form');
 
// using addEventListener to bind the named 
// function (changeHandler) as the event-
// handler for the 'change' event:
formElement.addEventListener('change',changeHandler);

function changeHandler(event) {
  var form = this,changed = event.target;
 
  form.classList.toggle('hasInputChanged',changed.value !== changed.defaultValue);
 
}
 
var formElement = document.querySelector('form');
 
formElement.addEventListener('change',changeHandler);

form {
  border: 2px solid #000;
  padding: 1em;
}
form.hasInputChanged {
  border-color: limegreen;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<form action="#" method="post">
  <fieldset>
    <legend>Simple demo</legend>
    <label for="name">Text Input:</label>
    <input type="text" name="name" id="name" value="" tabindex="1" />
  </fieldset>
</form>

外部JS Fiddle demo,用于实验或开发.

参考文献：

> CSS：

> Attribute selectors.

> JavaScript：

> document.querySelector().
> Element.classList.
> EventTarget.addEventListener().
> HTMLInputElement.

> jQuery：

> addClass().
> change().
> closest().
> on().
> toggleClass().

jQuery查找前提？

解决方法

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