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Vue how to send index from v-for to method

I'm trying to pass the index of a v-for so i can change some values, i'm adding the doctor team members dynamically and i have this file input to add their image, although when i add doctors it only changes the first's one image because it always sends index of the first doctor, the file input is inside the v-for loop if that helps.
<v-file-input
hide-input
class="d-none"
id="doctorImage"
truncate-length="1"
#change="doctorImage($event, index, doctor)"
></v-file-input>
Method:
doctorImage(e, index, doctor) {
console.log(index)
this.doctors[index] = {
image: URL.createObjectURL(e),
imageData: e,
name: doctor.name,
specialty: doctor.specialty
}
this.doctorChange += 1
}
The index is always 0, although it displays the index number when i create it dynamically on the doctor's card, why is that happening?

Refer List Rendering using v-for.
<div ... v-for="(doctor, index) in doctors" ... >
{{ index }} // you can use index
...
</div>

Ok so i fixed the issue, that happened because i had a label for doctorImage and the file input id was doctorImage also inside the v-for statement, that made multiple same id's and created a conflict.

I iterate with a limit. Example
If the data were:
{
limit: 3,
currentIndex: 2,
listData:[{name:'Data1'},{name:'Data2'},{name:'Data3'},{name:'Data4'},{name:'Data5'}]
}
In the .vue file it would be the following
<span v-for="index in limit" v-bind:key="index">
{{listData[index+currentIndex].name}}
</span>
I make sure that you control that the sum index + currentIndex does not exceed the limit of your data

How to define a temporary variable in Vue.js template

Here is my current template:
<a-droppable v-for="n in curSize" :key="n - 1" :style="{width: `${99.99 / rowLenMap[orderList[n - 1]]}%`, order: orderList[n - 1]}">
<a-draggable :class="{thin: rowLenMap[orderList[n - 1]] > 10}">
<some-inner-element>{{rowLenMap[orderList[n - 1]]}}</some-inner-element>
</a-draggable>
</a-droppable>
The problem is that i have to write rowLenMap[orderList[n - 1]] multiple times, and i'm afraid vue.js engine will also calculate it multiple times.
What i want is something like this:
<a-droppable v-for="n in curSize" :key="n - 1" v-define="rowLenMap[orderList[n - 1]] as rowLen" :style="{width: `${99.99 / rowLen}%`, order: orderList[n - 1]}">
<a-draggable :class="{thin: rowLen > 10}">
<some-inner-element>{{rowLen}}</some-inner-element>
</a-draggable>
</a-droppable>
I think it's not difficult to implement technically because it can be clumsily solved by using something like v-for="rowLen in [rowLenMap[orderList[n - 1]]]". So is there any concise and official solution?

I found a very simple (almost magical) way to achieve that,
All it does is define an inline (local) variable with the value you want to use multiple times:
<li v-for="id in users" :key="id" :set="user = getUser(id)">
<img :src="user.avatar" />
{{ user.name }}
{{ user.homepage }}
</li>
Note : set is not a special prop in Vuejs, it's just used as a placeholder for our variable definition.
Source: https://dev.to/pbastowski/comment/7fc9
CodePen: https://codepen.io/mmghv/pen/dBqGjM
Update : Based on comments from #vir us
This doesn't work with events, for example #click="showUser(user)" will not pass the correct user, rather it will always be the last evaluated user, that's because the user temp variable will get re-used and replaced on every circle of the loop.
So this solution is only perfect for template rendering because if component needs re-render, it will re-evaluate the variable again.
But if you really need to use it with events (although not advisable), you need to define an outer array to hold multiple variables at the same time :
<ul :set="tmpUsers = []">
<li v-for="(id, i) in users" :key="id" :set="tmpUsers[i] = getUser(id)" #click="showUser(tmpUsers[i])">
<img :src="tmpUsers[i].avatar" />
{{ tmpUsers[i].name }}
{{ tmpUsers[i].homepage }}
</li>
</ul>
https://codepen.io/mmghv/pen/zYvbPKv
credits : #vir us
Although it doesn't make sense here to basically duplicate the users array, this could be handy in other situations where you need to call expensive functions to get the data, but I would argue you're better off using computed property to build the array then.

Judging by your template, you're probably best off with a computed property, as suggested in the accepted answer.
However, since the question title is a bit broader (and comes up pretty high on Google for "variables in Vue templates"), I'll try to provide a more generic answer.
Especially if you don't need every item of an array transformed, a computed property can be kind of a waste. A child component may also be overkill, in particular if it's really small (which would make it 20% template, 20% logic and 60% props definition boilerplate).
A pretty straightforward approach I like to use is a small helper component (let's call it <Pass>):
const Pass = {
render() {
return this.$scopedSlots.default(this.$attrs)
}
}
Now we can write your component like this:
<Pass v-for="n in curSize" :key="n - 1" :rowLen="rowLenMap[orderList[n - 1]]" v-slot="{ rowLen }">
<a-droppable :style="{width: `${99.99 / rowLen}%`, order: orderList[n - 1]}">
<a-draggable :class="{thin: rowLen > 10}">
<some-inner-element>{{rowLen}}</some-inner-element>
</a-draggable>
</a-droppable>
</Pass>
<Pass> works by creating a scoped slot. Read more about scoped slots on the Vue.js documentation or about the approach above in the dev.to article I wrote on the topic.
Appendix: Vue 3
Vue 3 has a slightly different approach to slots. First, the <Pass> component source code needs to be adjusted like this:
const Pass = {
render() {
return this.$slots.default(this.$attrs)
}
}

Today I needed this and used <template> tag and v-for like this
I took this code and
<ul>
<li v-for="key in keys"
v-if="complexComputation(key) && complexComputation(key).isAuthorized">
{{complexComputation(key).name}}
</li>
</ul>
Changed it to this
<ul>
<template v-for="key in keys">
<li v-for="complexObject in [complexComputation(key)]"
v-if="complexObject && complexObject.isAuthorized">
{{complexObject.name}}
</li>
</template>
</ul>
And it worked and I was pleasantly surprised because I didn't know this was possible

This seems like the perfect use case of a child component. You can simply pass your complex computed value(s) as a property to the component.
https://v2.vuejs.org/v2/guide/components.html#Passing-Data-to-Child-Components-with-Props

How about this:
<div id="app">
<div
v-for="( id, index, user=getUser(id) ) in users"
:key="id"
>
{{ user.name }}, {{ user.age }} years old
<span #click="show(user)">| Click to Show {{user.name}} |</span>
</div>
</div>
CodePen: https://codepen.io/Vladimir-Miloevi/pen/xxJZKKx

<template>
<div>
<div v-for="item in itemsList" :key="item.id">
{{ item.name }}
<input v-model="item.description" type="text" />
<button type="button" #click="exampleClick(item.id, item.description)">
Click
</button>
</div>
</div>
</template>
<script>
export default {
data() {
return {
items: [
{
id: 1,
name: 'Name1',
},
{
id: 2,
name: 'Name2',
},
],
}
},
computed: {
itemsList() {
return this.items.map((item) => {
return Object.assign(item, { description: '' })
})
},
},
methods: {
exampleClick(id, description) {
alert(JSON.stringify({ id, description }))
},
},
}
</script>

Just tested using vue3 and works, i think it works universally
{{ (somevariable = 'asdf', null) }}
<span v-if="somevariable=='asdf'">Yey</span>
<span v-else>Ney</span>
It outputs nothing while setting your variable.
mandatory:
opening "("
set your variable
closing ", null)"

curSize is an array. Your temporary values comprise a corresponding implied array sizedOrderList = curSize.map(n => orderList[n-1]). If you define that as a computed, your HTML becomes
<a-droppable v-for="n, index in sizedOrderList" :key="curSize[index]" :style="{width: `${99.99 / rowLenMap[n]}%`, order: n}">
<a-draggable :class="{thin: rowLenMap[n] > 10}">
<some-inner-element>{{rowLenMap[n]}}</some-inner-element>
</a-draggable>
</a-droppable>

VueJS v-for loop breaking when array values are equal to each other

my pen: http://codepen.io/leetzorr/pen/aprZqO
html
<template v-for="spot in bars" :key="item.$index">
<div id="bar-holder">
<div class="bars">
<ul>
<span>{{ $index }}</span>
<li v-for="n in bars[$index]"></li>
</ul>
<button v-on:click="increase($index)">+</button>
</div>
</div>
</template>
javascript
var par = {
bars : [ 1, 5, 6 ]
}
var cl = new Vue({
el: '#container',
data: par,
methods: {
increase: function (index) {
var value = this.bars[index];
value++;
par.bars.$set(index, value);
},
}
})
So whenever you click the increase button under each group of bars, that value in the par.bars array increases. For some reason, whenever par.bar[index]'s value equals that of one of its siblings, one of the bar elements disappears.
I've went over my code for about an hour now, and cannot figure out where this is breaking.

Replace
<template v-for="spot in bars" :key="spot.$index">
with:
<template v-for="spot in bars" :key="spot.$index" track-by="$index">
Explanation in the Vue.js guide: http://v1.vuejs.org/guide/list.html#track-by-index

This is because Vue reuse templates with same key.
To avoid that you could use index as key (apparently that was you were trying to do in first place!)
Change your template's directive v-for to something like this
<template v-for="spot in bars.length">
Please see this working fiddle

Vue.js -- How to prevent data modification between components

I must say I'm still pretty new to Vue.js.
I build a Point of Sale system with the help of this tutorial.
I have made some modifications to it, for example the items are
fetched with an api call and you now can edit the price of an item in the transaction. It also required some fixing after updating to latest vue version, for example v-repeat to v-for etc.
Now I have a problem that is if you edit the price of an item in the transaction
it also changes the price of the item in the item list where you click to add the items.
Due to reasons I can't provide a whole image of the app or large parts of code.
Here's a screencap trying to explain what's happening
In the item list template the items are rendered from items array with v-for.
In the transaction template the items are rendered from itemList array with v-for.To clarify: itemList array contains the items added to the transaction.
I can't understand why this is happening or better yet how to prevent it. I can consider providing parts of the code if you need it.
EDIT:
In the comments Hector guessed that I'm referencing the same array in both of the templates, but that is not the case.
In the item list component I reference the items array by passing a prop.
<item-list :items="items" :add="onItemClick"></item-list>
In the transaction component I reference the lineItems array by passing a prop.
<transaction :items="lineItems" :edit-number-of-items="editNumberOfItems" :edit-price-each="editPriceEach" :edit-total-qty="editTotalQty" :edit-taxed-price="editTaxedPrice" :editing="editing" :remove-item="removeItem"></transaction>
The first three cells of the transaction table:
<tbody>
<tr v-for="item in items">
<!-- Code -->
<td>{{ item.item.id }}</td>
<!-- Name -->
<td>
<span>{{ item.item.name }}</span>
</td>
<!-- Price Each -->
<td>
<span class="editable-item" v-if="!item.editingPriceEach" #click="editPriceEach(item)">{{ item.item.priceEach }}</span>
<input v-if="item.editingPriceEach" #keyup.enter="editPriceEach(item)" type="text" v-model="item.item.priceEach" autofocus>
<button v-if="item.editingPriceEach" #click="editPriceEach(item)">OK</button>
</td>
In <tr v-for="item in items"> items is referring to the prop name items not the array called items in the data option.
Also for example the function editPriceEach passed to the transaction component as a prop looks like this:
editPriceEach: function (lineItem) {
lineItem.editingPriceEach = !lineItem.editingPriceEach;
}
As you can see it triggers the editingPriceEach property which is then used in the onItemClick function. It's used to add the items from the item list to the transaction:
onItemClick: function (item) {
var found = false;
for (var i = 0; i < this.lineItems.length; i++) {
if (this.lineItems[i].item === item) {
this.lineItems[i].numberOfItems++;
found = true;
break;
}
}
if (!found) {
this.lineItems.push({
item: item,
numberOfItems: 1,
editingNumberOfItems: false,
editingName: false,
editingPriceEach: false,
editingTaxedPrice: false,
editingTotalQty: false
});
}
},
Thank you for your patience with the small amount of code.

VueJs: How to Edit an Array Item

Simple Todo-App. Please excuse my ignorance for making a rather basic question.
But how would you go about and edit a certain item on an array?
Normally I would try to bind the value of my input to a new property on my data object and then assign this new property to the old property on click throuch Vue's two way databinding.
Like this: http://jsfiddle.net/z7960up7/
Well in my case I use the v-repeat directive, which loops through my data array but I can't use the v-model directive to use the two way databinding, because the values of the properties get corrupted if I do so. (See here: http://jsfiddle.net/doL46etq/2/)
And now I wonder, how I would go about updating my array of tasks:
My idea is to pass the VueObject (this) through my method on click, and then define the index on my event handler and then updating the tasks array, using the index, like this:
HTML:
<input v-el="editInputField" type="text" value="{{ task.body }}" v-on="keyup: doneEdit(this) | key 'enter'"/>
<button v-on="click: editTask(this)">
Edit
</button>
JS:
methods: {
editTask: function (task) {
var taskIndex = this.tasks.indexOf(task.task);
this.tasks[taskIndex] = {
'body': document.querySelector('input').value,
'completed': false
};
console.log(task.task.body);
},
}
Here is my fiddle about it:
http://jsfiddle.net/doL46etq/3/
But the data object is not updated at all and I wonder how I would go about it and update it.
What is the best way to edit an element on the array, using Vue?
Edit: An easy way, would just be to delete the element, and add the new to the array, using the push method, but I really want just to update the element, because I like to keep the dataobject in sync with my backend.

The short answer: Use a component in an extended constructor, then pass the index to that component in HTML as property and use computed properties to link back and forth to your data.
But don't be satisfied with just the short answer. Here is the long one:
Situation: I am using your JSFiddle as base for this answer.
in HTML you have:
<td>{{ task.body }}</td>
<td>
<div>
<input v-el="editInputField" type="text" value="{{ task.body }}" v-on="keyup: doneEdit(this) | key 'enter'" v-model="newEdit"/>
</div>
</td>
<td>
<button v-on="click: editTask(this)" class="mdl-button mdl-js-button mdl-button--icon"> <i class="material-icons">create</i>
</button>
</td>
We want to replace this code with the component. Using this component allows us to identify the index/row we are working on in your set of data.
<td v-component="listitem" index="{{$index}}"></td>
Next step: defining the component.
In order not to cloud our instance with the component, we will create a separate constructor for the vue object, so we can assign the new element to our new object.
This is done using extend.
window.newVue = Vue.extend({
components:
{
'listitem': {
props: ['index'],
computed: {
// both get and set
body: {
get: function () {
return this.$parent.tasks[this.index].body;
},
set: function (v) {
this.$parent.tasks[this.index].body = v
}
}
},
template: '<td>{{ body }}</td><td><div><input type="text" v-model="body" value="{{ body }}"/></div></td><td></td>',
}
}
});
Since we can't define our data properly using an extend, we'll just assume the data already exists while writing the component.
Step 3: defining the actual data:
Instead of using Vue as our object constructor, we'll now use our newly created instantiator.
new newVue({
el: '#todoapp',
data: {
tasks: [{
'body': 'Eat breakfast',
'completed': false
}, {
'body': 'Drink milk',
'completed': false
}, {
'body': 'Go to the store',
'completed': false
}],
newTask: '',
},
});
That's it!
In case you couldn't follow what happened: Here's the Fiddle!
PS: More information about the working of these code can be found on vuejs.org

Actually the simplest way to update an array item, is to two-way bind the task body with the v-model directive.
Example:
http://jsfiddle.net/z7960up7/2/
<div id="demo">
{{ message }}
<div class="edit">
<input type="text" v-model="message">
<button v-on="click: editMessage">Edit</button>
</div>
<pre>{{ $data | json }}</pre>
</div>
And fire an event whenever you blur out of the input box or the edit button is hit.
Also hide the input field with css, by using the v-class directive.