jQuery找到了先行者？

Question

当我想找到一个我可以使用的物体的孩子时children(); 当我想在另一个对象中找到一个对象时,不一定是它的孩子,我可以使用find().如果我想找一个父母,我会用parent(),但如果我想找到一个先行者,不知道它是否是父母祖父母,曾祖父母,我该怎么办呢？

我将举一个例子:我正在构建一个适用于某些'input:text'的插件.

最后,我需要对包含它们的形式做一些事情.但有时,文本框将直接位于表单内部,或者它们可以位于无序列表内或表内.

我能以一般方式参考表格吗？

Answer 1

你可以使用jQuery的closest()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小提琴演示,用于实验或开发.

或者,相反,你可以简单地使用其相关联的DOM方法<form>元素及其后代的形式元素(<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小提琴演示,用于实验或开发.

此外,因为我强烈怀疑你想要改变 - 无论它们是什么 - 如果"改变"被撤消还原,我建议采用以下方法:

$('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小提琴演示,用于实验或开发.

此外,完全可以使用以下命令将change事件处理程序委托给<form>元素本身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小提琴演示,用于实验或开发.

也可以将选择器传递给on()方法,以指定应该启动给定事件的元素(这里是'change'事件)以触发绑定到祖先的事件处理:

// 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', changedEl.value !== changedEl.defaultValue);
});

$('form').on('change', 'input[type=text]', 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小提琴演示,用于实验或开发.

最后,一个简单的JavaScript意味着完成相同的行为:

// 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小提琴演示,用于实验或开发.

参考文献:

• CSS:
  • 属性选择器.
• JavaScript的:
  • document.querySelector().
  • Element.classList.
  • EventTarget.addEventListener().
  • HTMLInputElement.
• jQuery的:
  • addClass().
  • change().
  • closest().
  • on().
  • toggleClass().