.prop()
.prop( propertyName )
描述：获得匹配的元素集合中第一个元素的某个属性的值。
The .prop() method gets the property value for only the first element in the matched set. It returns undefined for the value of a property that has not been set, or if the matched set has no elements. To get the value for each element individually, use a looping construct such as jQuery's .each() or .map() method.
注意： Attempting to change the type property (or attribute) of an input element created via HTML or already in an HTML document will result in an error being thrown by Internet Explorer 6, 7, or 8.
元素属性和属性的对比
The difference between attributes and properties can be important in specific situations. Before jQuery 1.6, the .attr()method sometimes took property values into account when retrieving some attributes, which could cause inconsistent behavior. As of jQuery 1.6, the .prop() method provides a way to explicitly retrieve property values, while .attr() retrieves attributes.
For example, selectedIndex, tagName, nodeName, nodeType, ownerDocument, defaultChecked, and defaultSelected should be retrieved and set with the .prop() method. Prior to jQuery 1.6, these properties were retrievable with the .attr() method, but this was not within the scope of attr. These do not have corresponding attributes and are only properties.
Concerning boolean attributes, consider a DOM element defined by the HTML markup <input type="checkbox" checked="checked" />, and assume it is in a JavaScript variable named elem:
elem.checked | true (Boolean) Will change with checkbox state |
|---|---|
$( elem ).prop( "checked" ) | true (Boolean) Will change with checkbox state |
elem.getAttribute( "checked" ) | "checked" (String) Initial state of the checkbox; does not change |
$( elem ).attr( "checked" ) (1.6) | "checked" (String) Initial state of the checkbox; does not change |
$( elem ).attr( "checked" ) (1.6.1+) | "checked" (String) Will change with checkbox state |
$( elem ).attr( "checked" ) (pre-1.6) | true (Boolean) Changed with checkbox state |
According to the W3C forms specification, the checked attribute is a boolean attribute, which means the corresponding property is true if the attribute is present at all—even if, for example, the attribute has no value or is set to empty string value or even "false". This is true of all boolean attributes.
Nevertheless, the most important concept to remember about the checked attribute is that it does not correspond to the checked property. The attribute actually corresponds to the defaultChecked property and should be used only to set theinitial value of the checkbox. The checked attribute value does not change with the state of the checkbox, while the checkedproperty does. Therefore, the cross-browser-compatible way to determine if a checkbox is checked is to use the property:
if ( elem.checked )if ( $( elem ).prop( "checked" ) )if ( $( elem ).is( ":checked" ) )
对于其它动态元素属性来说也一样，比如说selected和value。
其它说明
- In Internet Explorer prior to version 9, using
.prop()to set a DOM element property to anything other than a simple primitive value (number, string, or boolean) can cause memory leaks if the property is not removed (using.removeProp()) before the DOM element is removed from the document. To safely set values on DOM objects without memory leaks, use.data().
示例
显示勾选框的checked属性和元素属性，与此同时改它的勾中状态。
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>prop demo</title>
<style>
p {
margin: 20px 0 0;
}
b {
color: blue;
}
</style>
<script src="https://code.jquery.com/jquery-1.10.2.js"></script>
</head>
<body>
<input id="check1" type="checkbox" checked="checked">
<label for="check1">Check me</label>
<p></p>
<script>
$( "input" ).change(function() {
var $input = $( this );
$( "p" ).html(
".attr( \"checked\" ): <b>" + $input.attr( "checked" ) + "</b><br>" +
".prop( \"checked\" ): <b>" + $input.prop( "checked" ) + "</b><br>" +
".is( \":checked\" ): <b>" + $input.is( ":checked" ) ) + "</b>";
}).change();
</script>
</body>
</html>
演示结果
.prop( propertyName )
描述：针对匹配的元素集合设置一个或多个属性。
- properties类型：PlainObject一个对象，它是要设置的属性名值对。
The .prop() method is a convenient way to set the value of properties—especially when setting multiple properties, using values returned by a function, or setting values on multiple elements at once. It should be used when setting selectedIndex, tagName, nodeName, nodeType, ownerDocument, defaultChecked, or defaultSelected. Since jQuery 1.6, these properties can no longer be set with the .attr() method. They do not have corresponding attributes and are only properties.
Properties generally affect the dynamic state of a DOM element without changing the serialized HTML attribute. Examples include the value property of input elements, the disabled property of inputs and buttons, or the checked property of a checkbox. The .prop() method should be used to set disabled and checked instead of the .attr() method. The .val()method should be used for getting and setting value.
$( "input" ).prop( "disabled", false ); $( "input" ).prop( "checked", true ); $( "input" ).val( "someValue" );
重要： the .removeProp() method should not be used to set these properties to false. Once a native property is removed, it cannot be added again. See .removeProp() for more information.
计算属性值
利用一个函数来设置值，你可以根据元素的其它属性值来计算。举个例子：基于每个勾选框的值，来切换所有勾选框的选中状态。
$( "input[type='checkbox']" ).prop( "checked", function( i, val ) {
return !val;
});
注意：如果设置器函数没有返回任何东西（亦即，function( index, prop ){})），或者如果返回了undefined，则不会改变当前值。当只需要对部分满足条件的元素有选择地设置值时，这个功能特别有用。
其它说明
- In Internet Explorer prior to version 9, using
.prop()to set a DOM element property to anything other than a simple primitive value (number, string, or boolean) can cause memory leaks if the property is not removed (using.removeProp()) before the DOM element is removed from the document. To safely set values on DOM objects without memory leaks, use.data().
示例
在网页上禁用所有的勾选框。
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>prop demo</title>
<style>
img {
padding: 10px;
}
div {
color: red;
font-size: 24px;
}
</style>
<script src="https://code.jquery.com/jquery-1.10.2.js"></script>
</head>
<body>
<input type="checkbox" checked="checked">
<input type="checkbox">
<input type="checkbox">
<input type="checkbox" checked="checked">
<script>
$( "input[type='checkbox']" ).prop({
disabled: true
});
</script>
</body>
</html>
演示结果