我想要实现的事情是，每当<select>下拉菜单被更改时，我想要更改前的下拉菜单的值。我使用1.3.2版本的jQuery和使用的变化事件，但我在那里得到的值是变化后。
<select name="test">
<option value="stack">Stack</option>
<option value="overflow">Overflow</option>
<option value="my">My</option>
<option value="question">Question</option>
</select>
让我们说当前选项My现在被选中，当我在onchange事件中将其更改为堆栈时(即当我将其更改为堆栈时)，我想要它之前的值，即在这种情况下我的期望。
如何实现这一目标?
编辑:在我的情况下，我有多个选择框在同一页，并希望同样的事情被应用到所有他们。也所有我的选择后插入页面加载通过ajax。
当前回答
我选择Avi Pinto的解决方案，它使用jquery.data()
使用焦点并不是一个有效的解决方案。它在你第一次改变选项时起作用，但如果你停留在选择元素上，并按“上”或“下”键。它不会再次通过焦点事件。
所以解应该是这样的，
//set the pre data, usually needed after you initialize the select element
$('mySelect').data('pre', $(this).val());
$('mySelect').change(function(e){
var before_change = $(this).data('pre');//get the pre data
//Do your work here
$(this).data('pre', $(this).val());//update the pre data
})
其他回答
手动跟踪值。
var selects = jQuery("select.track_me");
selects.each(function (i, element) {
var select = jQuery(element);
var previousValue = select.val();
select.bind("change", function () {
var currentValue = select.val();
// Use currentValue and previousValue
// ...
previousValue = currentValue;
});
});
如何使用一个自定义的jQuery事件与角手表类型的接口;
// adds a custom jQuery event which gives the previous and current values of an input on change
(function ($) {
// new event type tl_change
jQuery.event.special.tl_change = {
add: function (handleObj) {
// use mousedown and touchstart so that if you stay focused on the
// element and keep changing it, it continues to update the prev val
$(this)
.on('mousedown.tl_change touchstart.tl_change', handleObj.selector, focusHandler)
.on('change.tl_change', handleObj.selector, function (e) {
// use an anonymous funciton here so we have access to the
// original handle object to call the handler with our args
var $el = $(this);
// call our handle function, passing in the event, the previous and current vals
// override the change event name to our name
e.type = "tl_change";
handleObj.handler.apply($el, [e, $el.data('tl-previous-val'), $el.val()]);
});
},
remove: function (handleObj) {
$(this)
.off('mousedown.tl_change touchstart.tl_change', handleObj.selector, focusHandler)
.off('change.tl_change', handleObj.selector)
.removeData('tl-previous-val');
}
};
// on focus lets set the previous value of the element to a data attr
function focusHandler(e) {
var $el = $(this);
$el.data('tl-previous-val', $el.val());
}
})(jQuery);
// usage
$('.some-element').on('tl_change', '.delegate-maybe', function (e, prev, current) {
console.log(e); // regular event object
console.log(prev); // previous value of input (before change)
console.log(current); // current value of input (after change)
console.log(this); // element
});
这是对@thisisboris的回答的改进。它将当前值添加到数据中，因此代码可以控制设置为当前值的变量何时被更改。
(function()
{
// Initialize the previous-attribute
var selects = $( 'select' );
$.each( selects, function( index, myValue ) {
$( myValue ).data( 'mgc-previous', myValue.value );
$( myValue ).data( 'mgc-current', myValue.value );
});
// Listen on the body for changes to selects
$('body').on('change', 'select',
function()
{
alert('I am a body alert');
$(this).data('mgc-previous', $(this).data( 'mgc-current' ) );
$(this).data('mgc-current', $(this).val() );
}
);
})();
$("#dropdownId").on('focus', function () {
var ddl = $(this);
ddl.data('previous', ddl.val());
}).on('change', function () {
var ddl = $(this);
var previous = ddl.data('previous');
ddl.data('previous', ddl.val());
});
将焦点事件与更改事件结合起来以实现您想要的结果:
(function () {
var previous;
$("select").on('focus', function () {
// Store the current value on focus and on change
previous = this.value;
}).change(function() {
// Do something with the previous value after the change
alert(previous);
// Make sure the previous value is updated
previous = this.value;
});
})();
工作示例:http://jsfiddle.net/x5PKf/766
