I'm still pretty new to vue.js.
I recently created some vue components to tidy up my html. The components are different inputs like text and checkbox. They update the parents data using $emit('input', val). And make sure that the components are up-to-date using props and watch() on those props.
Now there is a problem with using watch() on <input type="file />, since you cannot set the input value like you can on other input types.
Using this example:
https://jsfiddle.net/minde281/nyu73dz6/25/
I have a list of, in this case, items on a shoppinglist. You can add an image for each item.
The image is loaded and added to the list. This works fine.
To get my problem:
add an image to item1
delete that item by clicking the X-button
The result is now that item2 will have that image on the <input type="file" />. The preview works as expected since this can be set through script and therefore use watch(). But somehow vue removes the wrong part of the html markup causing the last one to be removed.
Is there a different way to solve this problem? Or is there a way to tell vue to remove the correct part of the html markup?
-Minde
Vue tries to reuse the component and thats why the selected file is in the second input after deleting the component.
To prevent that you should use the key binding like this:
<li v-for="(item, index) in items" :key="item.name">
Now the hole component gets removed and everything should work as expected.
Related
I have a Nuxt 2.9.0 app where I'm using #nuxtjs/vuetify 1.11.3.
I'm refactoring some HTML tables that we have in the app and replacing them with Vuetify's v-data-table components. Now, in our old tables we had these bar chart components that we would render inside the table cells, like this:
<th>
{{ totalAvg }}
<RatingBar :color="ratingColor(totalAvg)" />
</th>
That RatingBar component is basically just an empty div with a background color, as you can see below
What's the proper way in which I can keep this functionality when moving onto the Vuetify data tables?
I know that Vuetify implements some slots, for example the #header slot, but I'm not sure exactly how the slots work when it comes to table cells, since the #header slot, for example, seems to just append whatever <template> you write down for the slot, instead of actually replacing the header
Vuetify's v-data-table supports custom rendering for a specific column thru #item.<name>. Link to API doc.
I still don't quite get the use of keys even after reading through the docs but I understand that it has to do with keeping each item unique. I've been solely adding a key when using a v-for and only to the outer most parent (not the children of the v-for. Are there any other situations when keys should be used?
<div v-for="(person,index) in people" :key="index>
<div class="name-label>
<img :src="person.img/>
<div> {{ person.name }} </div>
</div>
</div>
The key directive alongside v-for, is used to uniquely identify each parent element rendered on the v-for operation.
The same happens in Reactjs:
{elements.map((value, index) => {
return <li key={index}>{value}</li>
})}
The key directive in Vuejs is also used to force Vuejs to re-render an element that contains it every time :key receives a new value.
As #firmino-changani indicated, other uses of key is if you want Vue to force a re-render or replacement of an element or component. See key special attribute documentation:
It can also be used to force replacement of an element/component
instead of reusing it. This can be useful when you want to:
Properly trigger lifecycle hooks of a component
Trigger transitions For example:
<transition>
<span :key="text">{{ text }}</span>
</transition>
When text changes, the <span> will always be replaced instead of patched, so a transition will be triggered.
Another example, lets say you have a dialog popup to add new data and another component that needs updating once the new data was entered via the popup. This second component might have logic inside lifecycle hooks like onMounted etc. Using a :key you can force re-rending this component once the dialog popup is saved e.g.
<template>
<page>
<add-data-popup #save="myKey++" />
<show-data :key"myKey" />
</page>
</template>
From the vueJs docs around Keys:
The key special attribute is primarily used as a hint for Vue’s virtual DOM algorithm to identify VNodes when diffing the new list of nodes against the old list.
To simply put it, if a div is rendered via a For-loop the div will be identical to each other div. When a user clicks on one of these Div's and you instantiate a #click function, how will vueJs know what differentiates each of these divs? How will vue know how to reorder these div's in the correct order if you remove a middle div?
VueJs uses the key to know how to reorder the DOM when an action is taken on one of these objects in your For loop.
Here is an article fully explaining about vueJs keys, and more details on the VueJS reactivity engine which is good to know about: https://www.telerik.com/blogs/in-vue-when-do-i-actually-need-the-key-attribute-and-why
I have a prismic group (link_sections) containing a bunch of fields. One of the fields is a link, because the markup I am creating with these groups is supposed to contain a button that links elsewhere on the site. The problem is that I don't know how to use prismic links properly in this context because as far as I can tell it is not possible to bind the link data inside of a v-btn like so...
<v-layout v-for="(section, index) in fields.link_sections" :key="index">
<h2>{{section.header}}</h2>
<v-btn router-link :to="{{section.link}}"></v-btn>
</v-layout>
If I just render out {{section.link}} outside of the v-btn element I can render out the text value of the link successfully, but that's about as much as I can do and obviously I want to use the text as an actual link. Anyone know how I can make a link field from a prismic group work with a v-btn element?
Your syntax is wrong, try this snippet:
<v-btn :to="section.link">Link</v-btn>. Also <b-btn></v-btn> has not router-link prop. Just pass prop to. If you pass to prop, it implies that you want that button to be a <router-link>
Denotes the target route of the link.
So basically, when using components - the app root passed to the Vue instance gets replaced by whatever HTML is in the component. Is there a way to disable this and just nest the stuff Vue renders inside the app root instead?
for example - if index.html has a wrapper of
<div id="myVueApp"></div>
and I set el: "#myVueApp" on the Vue instance, the whole node will get removed and replaced by whatever I have in my template resulting in
<div id="myComponent">...</div>
Is there a way to make it into
<div id="myVueApp">
<div id="myComponent">...</div>
</div>
Should work. From what I understand, you want to have multiple parts of your Vue app to be splitted up in the rendered HTML output as well, more specifically into multiple divs.
I think this should work if you use multiple Vue instances.
Set up a structure in your HTML file and give them appropriate id's.
Then, create the Vue instances you want and assign each of them to their specific div using el.
However, I can't tell you if this is a good idea and follows the best practice..
Hope this helps!
I have Vue component which receives json data from props, after this render child components using v-for and pass this data as prop. Everything works fine until i try to remove one item from this list, when i remove it, it removes element incorrectly. In vue devtools i see that parent receives data correctly but not renders it properly. can anyone help me?
here is my code: https://gist.github.com/giokaxo/3d291b9b7b8ef97f81dc83799c430302
Use "key" attribute when rendering elements using v-for, for example:
<p v-for="(product, index) in order.products" :key="i">..</p>
The relevant documentation is here:
You can directly use v-for on a custom component, like any normal
element:
<my-component v-for="item in items" :key="item.id"></my-component>
In 2.2.0+, when using v-for with a component, a key is now required.
However, this won’t automatically
pass any data to the component, because components have isolated
scopes of their own. In order to pass the iterated data into the
component, we should also use props:
<my-component
v-for="(item, index) in items"
v-bind:item="item"
v-bind:index="index"
v-bind:key="item.id">
</my-component>
The reason for not automatically injecting item into the component is because that makes the component
tightly coupled to how v-for works. Being explicit about where its
data comes from makes the component reusable in other situations.
And here:
When Vue is updating a list of elements rendered with v-for, it by
default uses an “in-place patch” strategy. If the order of the data
items has changed, instead of moving the DOM elements to match the
order of the items, Vue will simply patch each element in-place and
make sure it reflects what should be rendered at that particular
index.
...
To give Vue a hint so that it can track each node’s identity, and thus
reuse and reorder existing elements, you need to provide a unique key
attribute for each item. An ideal value for key would be the unique id
of each item.