watcher events - Vuejs get old value when on change event

3 Answers

What is the most efficient way to deep clone an object in JavaScript?

Note: This is a reply to another answer, not a proper response to this question. If you wish to have fast object cloning please follow Corban's advice in their answer to this question.

I want to note that the .clone() method in jQuery only clones DOM elements. In order to clone JavaScript objects, you would do:

// Shallow copy
var newObject = jQuery.extend({}, oldObject);

// Deep copy
var newObject = jQuery.extend(true, {}, oldObject);

More information can be found in the jQuery documentation.

I also want to note that the deep copy is actually much smarter than what is shown above – it's able to avoid many traps (trying to deep extend a DOM element, for example). It's used frequently in jQuery core and in plugins to great effect.

v-model emit dropdown

Please refer to my snippet below. How can I get the old value of the changed model, in this case is the age in vuejs?

var app = new Vue({
   items:[{name:'long name One',age:21},{name:'long name Two',age:22}]
<script src=""></script>
<script src=""></script>

<table class="table table-cart" id="table1">
     <tr v-for="(item,index) in items">
       <td>{{}} :</td>       
         <input type="text" name="qty"

I am trying to use watch, but I am not able to find any help in watching the age an array of items.

Assuming that you have only variables and not any functions in your object, you can just use:

var newObject = JSON.parse(JSON.stringify(oldObject));

You'll need to store the old value manually. You could store it a lot of different ways. You could use a javascript object to store values for each textbox, or you could use a hidden field (I wouldn't recommend it - too html heavy), or you could use an expando property on the textbox itself, like this:

<input type="text" onfocus="this.oldvalue = this.value;" onchange="onChangeTest(this);this.oldvalue = this.value;" />

Then your javascript function to handle the change looks like this:

    <script type="text/javascript">
    function onChangeTest(textbox) {
        alert("Value is " + textbox.value + "\n" + "Old Value is " + textbox.oldvalue);