< input>上的jQuery Change事件元素 - 任何保留先前价值的方式？ [英] jQuery Change event on an <input> element - any way to retain previous value?

问题描述

我今天早上一直在搜索，我没有找到任何简单的解决方案...基本上，我想捕获一个输入元素的变化，但也知道以前的值。

I've been searching around this morning and I'm not finding any simple solutions... basically, I want to capture a change in an input element, but also know the previous value.

这是一个更改事件和一个简单形式的输入元素。显然，我可以用$（elem）.val（）获取新的值，但是我有一个偷偷摸摸的方法来获取以前的值？我没有看到jQuery API中的任何东西来做到这一点，但是也许有人已经这样做了，并且有一些提示？

Here's a change event and an input element in its simplest form. Clearly, I can get the new value with $(elem).val(), but is there a sneaky method I'm missing for getting the previous value? I don't see anything in the jQuery API to do this, but maybe someone's already done this and has some tips?

<script>
    $(document).ready(function(){
        $('#myInputElement').bind('change', function(){
            //var oldvalue = ???
            var newvalue = $(this).val();
        });
    });
</script>
<input id="myInputElement" type="text">

我不反对编写自己的解决方案，我只是想确保我没有重新创建这里的轮子。

I'm not against writing my own solution, I just want to make sure I'm not recreating the wheel here.

推荐答案

更好的方法是使用.data存储旧值。这将备份创建一个全局变量，您应该远离并保留元素中封装的信息。关于为什么Global Vars是坏的一个真实世界的例子被记录在案这里

A better approach is to store the old value using .data. This spares the creation of a global var which you should stay away from and keeps the information encapsulated within the element. A real world example as to why Global Vars are bad is documented here

例如

<script>
    //look no global needed:)

    $(document).ready(function(){
        // Get the initial value
       var $el = $('#myInputElement');
       $el.data('oldVal',  $el.val() );


       $el.change(function(){
            //store new value
            var $this = $(this);
            var newValue = $this.data('newVal', $this.val());
       })
       .focus(function(){
            // Get the value when input gains focus
            var oldValue = $(this).data('oldVal');
       });
    });
</script>
<input id="myInputElement" type="text">

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