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I've been doing some vuejs for almost a year now and I never really got animations and transitions to work, it seems very unclear to me how all this is supposed to work and today I decided to try and finally understand them but once again I am stuck, the transition simply won't work and I don't understand what I'm doing wrong.
Here is my code:

The HTML

<div id="app">
 <div class="row">
 <div class="container-fluid">
 <transition-group name="flip-list" tag="div" class="row horizontal-scroll">
 <div class="col-xs-12 col-md-2 col-lg-2 col-card" 
 v-for="(someCard, index) in someCards" v-bind:key="index">
 <div class="some-card" @click="changeOrder(someCard)">
 someCard.someTitle 
 </div>
 </div>
 </transition-group>
 </div>
 </div>
</div>

The JS

new Vue(
 el: "#app",
 data: 
 someCards: [
 
 order: 2,
 someTitle: 'Title 1'
 ,
 
 order: 2,
 someTitle: 'Title 2'
 ,
 
 order: 2,
 someTitle: 'Title 3'
 ,
 
 order: 3,
 someTitle: 'Title 4'
 ,
 
 order: 3,
 someTitle: 'Title 5'
 ,
 
 order: 1,
 someTitle: 'Title 6'
 ,
 
 order: 1,
 someTitle: 'Title 7'
 ,
 
 order: 1,
 someTitle: 'Title 8'
 ,
 
 order: 3,
 someTitle: 'Title 1'
 
 ]
 ,
 methods: 
 changeOrder(someCardData) 
 let newRandom = Math.floor(Math.random() * 3) + 1;
 while (newRandom === someCardData.order) 
 newRandom = Math.floor(Math.random() * 3) + 1;
 
 someCardData.order = newRandom;
 this.reorderList();
 ,
 reorderList() 
 this.someCards.sort(function(objA, objB) 
 return objA.order - objB.order;
 )
 ,
 
)

The CSS

/* default */
body 
 background: #20262E;
 padding: 20px;
 font-family: Helvetica;

#app 
 background: #fff;
 border-radius: 4px;
 padding: 20px;
 transition: all 0.2s;

/* bootstrap */
.row 
 display: -ms-flexbox;
 display: flex;
 -ms-flex-wrap: wrap;
 flex-wrap: wrap;
 margin-right: -15px;
 margin-left: -15px;

.col-1, .col-2, .col-3, .col-4, .col-5, .col-6, .col-7, .col-8, .col-9, .col-10, .col-11, .col-12, .col, .col-auto, .col-sm-1, .col-sm-2, .col-sm-3, .col-sm-4, .col-sm-5, .col-sm-6, .col-sm-7, .col-sm-8, .col-sm-9, .col-sm-10, .col-sm-11, .col-sm-12, .col-sm, .col-sm-auto, .col-md-1, .col-md-2, .col-md-3, .col-md-4, .col-md-5, .col-md-6, .col-md-7, .col-md-8, .col-md-9, .col-md-10, .col-md-11, .col-md-12, .col-md, .col-md-auto, .col-lg-1, .col-lg-2, .col-lg-3, .col-lg-4, .col-lg-5, .col-lg-6, .col-lg-7, .col-lg-8, .col-lg-9, .col-lg-10, .col-lg-11, .col-lg-12, .col-lg, .col-lg-auto, .col-xl-1, .col-xl-2, .col-xl-3, .col-xl-4, .col-xl-5, .col-xl-6, .col-xl-7, .col-xl-8, .col-xl-9, .col-xl-10, .col-xl-11, .col-xl-12, .col-xl, .col-xl-auto 
 position: relative;
 width: 100%;
 min-height: 1px;
 padding-right: 15px;
 padding-left: 15px;


/* my css */
.horizontal-scroll 
 overflow-x: auto;
 -ms-flex-wrap: nowrap;
 flex-wrap: nowrap;

.col-card 
 max-width: 14%;

.some-card 
 height: 220px;
 font-size: 16px;
 text-align: center;
 padding-right: 5px;
 margin-top: 5px;
 -webkit-box-shadow: 1px 1px 5px rgba(0,0,0,.1);
 box-shadow: 1px 1px 5px rgba(0,0,0,.1);
 border-radius: 2px;
 background: #fff;
 margin-bottom: 20px;
 position: relative;
 border-top-style: solid;

.flip-list-move 
 transition: transform 1s;

https://jsfiddle.net/eywraw8t/459088/

I am trying to have an animation triggered when I reorder a card in a list of cards aligned in a row. To change the position of a card, simply click on it. The reorder works but no transition is done.

I used this documentation
https://vuejs.org/v2/guide/transitions.html#List-Move-Transitions
and have seen a couple of fairly easy tutorials but I must be missing something. Can someone please check the code out and tell me what it is ?

Thanks

It's because you're using the index as a key. The index will always be the same for the same position even if the card changes. I'd give each card a unique id and then use that as a key instead ..

new Vue(
 el: "#app",
 data: 
 someCards: [
 id: 0,
 order: 2,
 someTitle: 'Title 1'
 ,
 
 id: 1,
 order: 2,
 someTitle: 'Title 2'
 ,
 
 id: 2,
 order: 2,
 someTitle: 'Title 3'
 ,
 
 id: 3,
 order: 3,
 someTitle: 'Title 4'
 ,
 
 id: 4,
 order: 3,
 someTitle: 'Title 5'
 ,
 
 id: 5,
 order: 1,
 someTitle: 'Title 6'
 ,
 
 id: 6,
 order: 1,
 someTitle: 'Title 7'
 ,
 
 id: 7,
 order: 1,
 someTitle: 'Title 8'
 ,
 
 id: 8,
 order: 3,
 someTitle: 'Title 1'
 
 ]
 ,
 methods: 
 changeOrder(someCardData) 
 let newRandom = Math.floor(Math.random() * 3) + 1;
 while (newRandom === someCardData.order) 
 newRandom = Math.floor(Math.random() * 3) + 1;
 
 someCardData.order = newRandom;
 this.reorderList();
 ,
 reorderList() 
 this.someCards.sort(function(objA, objB) 
 return objA.order - objB.order;
 )
 ,
 
)

/* default */

body 
 background: #20262E;
 padding: 20px;
 font-family: Helvetica;


#app 
 background: #fff;
 border-radius: 4px;
 padding: 20px;
 transition: all 0.2s;



/* bootstrap */

.row 
 display: -ms-flexbox;
 display: flex;
 -ms-flex-wrap: wrap;
 flex-wrap: wrap;
 margin-right: -15px;
 margin-left: -15px;


.col-1,
.col-2,
.col-3,
.col-4,
.col-5,
.col-6,
.col-7,
.col-8,
.col-9,
.col-10,
.col-11,
.col-12,
.col,
.col-auto,
.col-sm-1,
.col-sm-2,
.col-sm-3,
.col-sm-4,
.col-sm-5,
.col-sm-6,
.col-sm-7,
.col-sm-8,
.col-sm-9,
.col-sm-10,
.col-sm-11,
.col-sm-12,
.col-sm,
.col-sm-auto,
.col-md-1,
.col-md-2,
.col-md-3,
.col-md-4,
.col-md-5,
.col-md-6,
.col-md-7,
.col-md-8,
.col-md-9,
.col-md-10,
.col-md-11,
.col-md-12,
.col-md,
.col-md-auto,
.col-lg-1,
.col-lg-2,
.col-lg-3,
.col-lg-4,
.col-lg-5,
.col-lg-6,
.col-lg-7,
.col-lg-8,
.col-lg-9,
.col-lg-10,
.col-lg-11,
.col-lg-12,
.col-lg,
.col-lg-auto,
.col-xl-1,
.col-xl-2,
.col-xl-3,
.col-xl-4,
.col-xl-5,
.col-xl-6,
.col-xl-7,
.col-xl-8,
.col-xl-9,
.col-xl-10,
.col-xl-11,
.col-xl-12,
.col-xl,
.col-xl-auto 
 position: relative;
 width: 100%;
 min-height: 1px;
 padding-right: 15px;
 padding-left: 15px;



/* my css */

.horizontal-scroll 
 overflow-x: auto;
 -ms-flex-wrap: nowrap;
 flex-wrap: nowrap;


.col-card 
 max-width: 14%;


.some-card 
 height: 220px;
 font-size: 16px;
 text-align: center;
 padding-right: 5px;
 margin-top: 5px;
 -webkit-box-shadow: 1px 1px 5px rgba(0, 0, 0, .1);
 box-shadow: 1px 1px 5px rgba(0, 0, 0, .1);
 border-radius: 2px;
 background: #fff;
 margin-bottom: 20px;
 position: relative;
 border-top-style: solid;


.flip-list-move 
 transition: transform 1s;

<script src="https://cdn.jsdelivr.net/npm/vue@2.5.17/dist/vue.js"></script>

<div id="app">
 <div class="row">
 <div class="container-fluid">
 <transition-group name="flip-list" tag="div" class="row horizontal-scroll">
 <div class="col-xs-12 col-md-2 col-lg-2 col-card" v-for="(someCard, index) in someCards" v-bind:key="someCard.id">
 <div class="some-card" @click="changeOrder(someCard)">
 someCard.someTitle 
 </div>
 </div>
 </transition-group>
 </div>
 </div>
</div>

JSFiddle