jQuery .prop() 返回未定义，而 .attr() 对数据按预期工作-* [英] jQuery .prop() returns undefined, while .attr() works as expected for data-*

问题描述

我只是想从两个元素中获取几个属性.从 input 元素获取属性 value 按预期工作.问题在于从 button 元素获取属性 data-detail 属性.它在使用 .prop() 时返回 undefined，但在使用 .attr() 时按预期工作.

谁能解释一下我目睹的这种奇怪的行为?

HTML

<label for="firstName">名字</label><div class="detailsControlBtns"><button id="editFirstName" class="btn ctaBtn greenBtn editBtn">编辑</button><button class="btn ctaBtn greenBtn saveBtn" data-detail="firstName">保存</button><button id="closeFirstName" class="btn ctaBtn greyBtn closeBtn">关闭</button>
<input type="text" id="firstName" name="firstName" value="[+firstName+]" readonly>

JS

$(".saveBtn").on("click", function() {var saveBtn = $(this);//以下语句产生未定义.使用 .attr() 时，它按预期工作.var detail = saveBtn.prop("data-detail");var relatedInput = saveBtn.parent().next();//以下语句按预期工作.var value = relatedInput.prop("value");//...});

解决方案

那是因为 HTML 元素上没有 data-detail property.

这里是对.data()的简要说明，.prop() 和 .attr() :

DOM 元素是一个对象，它具有methods 和properties(来自DOM) 和 attributes(来自呈现的 HTML).其中一些 properties 通过 attributes
id->id, class->className, 获得它们的 initial value标题->标题、样式->样式等

考虑这个元素: <input type="checkbox" checked data-detail="somedata" >

以下的结果是:

$('input').prop('id');//=>" "-空字符串，元素上存在属性 id(由 DOM 定义)，但未设置.$('input').attr('id');//=>未定义 - 不存在.

<小时>如果您执行以下操作:

$('input').attr('id',"someID");$('input').prop('id');//=>某个ID"$('输入').attr('id');//=>某个ID"

还有:

$('input').prop('id',"someOtherID");$('input').prop('id');//=>其他 ID"$('input').attr('id');//=>其他 ID"

<块引用>

因此，某些属性和属性具有1:1 映射.(的变化prop 的 attr 结果变化，反之亦然).

<小时>考虑以下几点:

$('input').prop('value');//=>一些价值"$('输入').val();//=>一些价值"$('输入').attr('值');//=>一些价值"

如果你这样做了:

$('input').prop('value','newVal');//或者$('input').val('newVal');$('输入').prop('值');//=>"newVal" - 属性值$('输入').val();//=>"newVal" - 属性值$('输入').attr('值');//=>"someValue" - attr 的值没有改变，因为在这种情况下它不是 1:1 映射(prop 值的变化不会反映到属性值).

<小时>

案例 .data()

1) 获取方式:

- 记住 attribute name 是 data-* 而 property name 是 dataset，所以:

 

 $('input')[0].dataset;//=>[对象 DOMStringMap] { 详细信息:一些数据"}$('输入')[0].dataset.detail;//=>一些数据"$('输入').prop('数据集');//=>[object DOMStringMap] { detail: "somedata"}$('input').prop('dataset').detail;//=>一些数据"$('输入').data('详细信息');//=>一些数据"$('input').attr('data-detail');//=>一些数据"

2) 如何设置:

I) $('input').prop('dataset').detail='newData';

 $('input').prop('dataset');//=>[对象 DOMStringMap] { 详细信息:新数据"}$('input').prop('dataset').detail;//=>新数据"$('input').attr('data-detail');//=>新数据"$('输入').data('详细信息');//=>新数据"

II) $('input').attr('data-detail','newData');

 $('input').prop('dataset');//=>[对象 DOMStringMap] { 详细信息:新数据"}$('input').prop('dataset').detail;//=>新数据"$('input').attr('data-detail');//=>新数据"$('输入').data('详细信息');//=>新数据"

<块引用>

所以你可以看到这里是 1:1 映射，attr 变化反映了 prop 和反之亦然.

但是检查第三种方式:

III) $('input').data('detail','newData');

 $('input').prop('dataset');//=>[对象 DOMStringMap] { 详细信息:一些数据"}$('input').prop('dataset').detail;//=>一些数据"$('input').attr('data-detail');//=>一些数据"$('输入').data('详细信息');//=>新数据"<----******

那么，这里发生了什么?

<块引用>

$(elem).data(key, value) 不会改变 HTML5 data-* 属性元素的.它在内部将其值存储在 $.cache 中.

所以为了获得 data-* 你永远不会出错 .data() :

$(".saveBtn").on("click", function() {var saveBtn = $(this);var detail = saveBtn.data("detail");var relatedInput = saveBtn.parent().next();var value = relatedInput.prop("value");});

I am simply trying to get a couple of properties from two elements. Getting the property value from the input element works as expected. The problem is with getting the property data-detail property from the button element. It returns undefined when using .prop(), but works as expected when using .attr().

Can anyone explain this odd behaviour I am witnessing?

HTML

<div class="formRow">
    <label for="firstName">First name</label>
    <div class="detailsControlBtns">
        <button id="editFirstName" class="btn ctaBtn greenBtn editBtn">Edit</button>
        <button class="btn ctaBtn greenBtn saveBtn" data-detail="firstName">Save</button>
        <button id="closeFirstName" class="btn ctaBtn greyBtn closeBtn">Close</button>
    </div>
    <input type="text" id="firstName" name="firstName" value="[+firstName+]" readonly>
</div>

JS

$(".saveBtn").on("click", function() {
    var saveBtn = $(this);
    // The following statement yields undefined. When using .attr() it works as expected.
    var detail = saveBtn.prop("data-detail");
    var relevantInput = saveBtn.parent().next();
    // The following statement works as expected.
    var value = relevantInput.prop("value");
    // ...
});

解决方案

That's because there's no data-detail property on HTML element.

Here is a quick explanation for .data(), .prop() and .attr() :

DOM element is an object which has methods, and properties (from the DOM) and attributes(from the rendered HTML). Some of those properties get their initial value by the attributes
id->id, class->className, title->title, style->style etc.

Consider this element: <input type="checkbox" checked data-detail="somedata" >

The result of the following would be:

$('input').prop('id'); // => " "-empty string, property id exist on the element (defined by DOM) , but is not set.
$('input').attr('id');// => undefined - doesn't exist.

---

If you do the following:

$('input').attr('id',"someID");
$('input').prop('id'); // =>  "someID"
$('input').attr('id'); // =>  "someID"

And also:

$('input').prop('id',"someOtherID");
$('input').prop('id');// =>  "someOtherID"
$('input').attr('id');// =>  "someOtherID"

So, some attributes and properties have 1:1 mapping. (change of the attr result change of the prop and vice versa).

---

Consider the following: <input type="text" data-detail="somedata" value="someValue">

$('input').prop('value'); // =>  "someValue"
$('input').val();         // =>  "someValue"
$('input').attr('value'); // =>  "someValue"

And if you do:

$('input').prop('value','newVal');

// or

$('input').val('newVal');

$('input').prop('value'); // => "newVal"    -value of the property
$('input').val();         // => "newVal"    -value of the property
$('input').attr('value'); // => "someValue" -value of the attr didn't change, since in this case it is not 1:1 mapping (change of the prop value doesn't reflect to the attribute value).

---

Case with the .data()

1) How to get:

- Have in mind that attribute name is data-* and property name is dataset, so:

<input type="checkbox" data-detail="somedata" > 

 

 $('input')[0].dataset; //=> [object DOMStringMap] { detail: "somedata"}
 $('input')[0].dataset.detail; // => "somedata"
 $('input').prop('dataset'); //=>[object DOMStringMap] { detail: "somedata"}
 $('input').prop('dataset').detail; // => "somedata"
 $('input').data('detail'); // => "somedata"
 $('input').attr('data-detail');  //  => "somedata"

2) How to set:

I) $('input').prop('dataset').detail='newData';

 $('input').prop('dataset');  //=> [object DOMStringMap] { detail: "newData"}
 $('input').prop('dataset').detail; // => "newData"
 $('input').attr('data-detail'); // => "newData"
 $('input').data('detail'); // => "newData"

II) $('input').attr('data-detail','newData');

 $('input').prop('dataset');  //=> [object DOMStringMap] { detail: "newData"}
 $('input').prop('dataset').detail; // => "newData"
 $('input').attr('data-detail'); // => "newData"
 $('input').data('detail'); // => "newData"

So you can see that here is 1:1 mapping, attr change reflects prop and vice versa.

But check the third way:

III) $('input').data('detail','newData');

 $('input').prop('dataset'); // =>  [object DOMStringMap] { detail: "somedata"}
 $('input').prop('dataset').detail; // => "somedata"
 $('input').attr('data-detail'); // => "somedata"
 $('input').data('detail');  // => "newData"    <-----******

So, what is happening up here?

$(elem).data(key, value) does not change the HTML5 data-* attributes of the element. It stores its values in $.cache internally.

So for getting data-* you would never go wrong with .data() :

$(".saveBtn").on("click", function() {
    var saveBtn = $(this);
    var detail = saveBtn.data("detail");
    var relevantInput = saveBtn.parent().next();
    var value = relevantInput.prop("value");

});

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