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How to access the correct `this` inside a callback
(13 answers)
Closed 1 year ago.
I have vue2 component where I want to access a data object variable to use in template. Pertinent code:
Template:
<div v-html="theWivesBios[currentWife]" class="modal-content"></div>
Script:
export default {
name: "theSixWives",
data() {
return {
theWivesBios: theWivesBios,
currentWife: ""
};
},
mounted() {
elContainer.addEventListener("click", function(ev) {
//Want to manipulate this.currentWife in callback
this.currentWife = "testing"; // this.currentWife isnt available to vue instance
}
What would be best way to "hoist" this.currentWife so the vue instance would have access to it for use in my template?
You have to use an arrow function like this:
export default {
name: "theSixWives",
data() {
return {
theWivesBios,
currentWife: ""
};
},
mounted() {
elContainer.addEventListener("click", () => {
this.currentWife = "testing";
});
}
}
This answer explains very well how this works on regular and arrow functions:
https://stackoverflow.com/a/20279485/7699022
Hope it helped!
Related
I was wondering if there is a way of creating computed props programatically, while still accessing the instance to achieve dynamic values
Something like that (this being undefined below)
<script>
export default {
computed: {
...createDynamicPropsWithTheContext(this), // helper function that returns an object
}
}
</script>
On this question, there is a solution given by Linus: https://forum.vuejs.org/t/generating-computed-properties-on-the-fly/14833/4 looking like
computed: {
...mapPropsModels(['cool', 'but', 'static'])
}
This works fine but the main issue is that it's fully static. Is there a way to access the Vue instance to reach upon props for example?
More context
For testing purposes, my helper function is as simple as
export const createDynamicPropsWithTheContext = (listToConvert) => {
return listToConvert?.reduce((acc, curr) => {
acc[curr] = curr
return acc
}, {})
}
What I actually wish to pass down to this helper function (via this) are props that are matching a specific prefix aka starting with any of those is|can|has|show (I'm using a regex), that I do have access via this.$options.props in a classic parent/child state transfer.
The final idea of my question is mainly to avoid manually writing all the props manually like ...createDynamicPropsWithTheContext(['canSubmit', 'showModal', 'isClosed']) but have them populated programatically (this pattern will be required in a lot of components).
The props are passed like this
<my-component can-submit="false" show-modal="true" />
PS: it's can-submit and not :can-submit on purpose (while still being hacked into a falsy result right now!).
It's for the ease of use for the end user that will not need to remember to prefix with :, yeah I know...a lot of difficulty just for a semi-colon that could follow Vue's conventions.
You could use the setup() hook, which receives props as its first argument. Pass the props argument to createDynamicPropsWithTheContext, and spread the result in setup()'s return (like you had done previously in the computed option):
import { createDynamicPropsWithTheContext } from './props-utils'
export default {
⋮
setup(props) {
return {
...createDynamicPropsWithTheContext(props),
}
}
}
demo
If the whole thing is for avoiding using a :, then you might want to consider using a simple object (or array of objects) as data source. You could just iterate over a list and bind the data to the components generated. In this scenario the only : used are in the objects
const comps = [{
"can-submit": false,
"show-modal": true,
"something-else": false,
},
{
"can-submit": true,
"show-modal": true,
"something-else": false,
},
{
"can-submit": false,
"show-modal": true,
"something-else": true,
},
]
const CustomComponent = {
setup(props, { attrs }) {
return {
attrs
}
},
template: `
<div
v-bind="attrs"
>{{ attrs }}</div>
`
}
const vm = Vue.createApp({
setup() {
return {
comps
}
},
template: `
<custom-component
v-for="(item, i) in comps"
v-bind="item"
></custom-component>
`
})
vm.component('CustomComponent', CustomComponent)
vm.mount('#app')
<script src="https://unpkg.com/vue#3"></script>
<div id="app">{{ message }}</div>
Thanks to Vue's Discord Cathrine and skirtle folks, I achieved to get it working!
Here is the thread and here is the SFC example that helped me, especially this code
created () {
const magicIsShown = computed(() => this.isShown === true || this.isShown === 'true')
Object.defineProperty(this, 'magicIsShown', {
get () {
return magicIsShown.value
}
})
}
Using Object.defineProperty(this... is helping keeping the whole state reactive and the computed(() => can reference some other prop (which I am looking at in my case).
Using a JS object could be doable but I have to have it done from the template (it's a lower barrier to entry).
Still, here is the solution I came up with as a global mixin imported in every component.
// helper functions
const proceedIfStringlean = (propName) => /^(is|can|has|show)+.*/.test(propName)
const stringleanCase = (string) => 'stringlean' + string[0].toUpperCase() + string.slice(1)
const computeStringlean = (value) => {
if (typeof value == 'string') {
return value == 'true'
}
return value
}
// the actual mixin
const generateStringleans = {
created() {
for (const [key, _value] of Object.entries(this.$props)) {
if (proceedIfStringlean(key)) {
const stringleanComputed = computed(() => this[key])
Object.defineProperty(this, stringleanCase(key), {
get() {
return computeStringlean(stringleanComputed.value)
},
// do not write any `set()` here because this is just an overlay
})
}
}
},
}
This will scan every .vue component, get the passed props and if those are prefixed with either is|can|has|show, will create a duplicated counter-part with a prefix of stringlean + pass the initial prop into a method (computeStringlean in my case).
Works great, there is no devtools support as expected since we're wiring it directly in vanilla JS.
I am building a web app with nuxt.
here's simplified code:
pages/index.vue
data() {
return {
item: {name:'', department: '', testField: '',},
}
}
async asyncData() {
const result = call some API
const dataToInitialize = {
name: result.username,
department: result.department,
testField: //want to assign computed value
}
return {item: dataToInitialize}
}
Inside asyncData, I call API and assign value to dataToInitialize.
dataToInitialize has testField field, and I want to assign some computed value based on username and department.
(for example, 'a' if name starts with 'a' and department is 'management'..etc there's more complicated logic in real scenario)
I have tried to use computed property , but I realized that asyncData cannnot access computed.
Does anyone know how to solve this?
Any help would be appreciated!
=======
not sure if it's right way, but I solved the issue by setting 'testfield' inside created.
created() {
this.item.testField = this.someMethod(this.item);
},
Looking at the Nuxt lifecyle, you can see that asyncData is called before even a Vue instance is mounted on your page.
Meanwhile, fetch() hook is called after. This is non-blocking but more flexible in a lot of ways.
An alternative using fetch() would look like this
<script>
export default {
data() {
return {
staticVariable: 'google',
}
},
async fetch() {
await this.$axios(this.computedVariable)
},
computed: {
computedVariable() {
return `www.${this.staticVariable}.com`
},
},
}
</script>
Another alternative, would be to use URL query string or params, thanks to Vue-router and use those to build your API call (in an asyncData hook).
Here is an example on how to achieve this: https://stackoverflow.com/a/68112290/8816585
EDIT after comment question
You can totally use a computed inside of a fetch() hook indeed. Here is an example on how to achieve this
<script>
export default {
data() {
return {
test: 'test',
}
},
async fetch() {
const response = await fetch(`https://jsonplaceholder.typicode.com/todos/${this.nice}`)
console.log(await response.json())
},
computed: {
nice() {
return this.test + 'wow!'
},
},
}
</script>
I found that destructuring fetch({}) causes issues with accessing this inside fetch scope ->
async fetch({ store, $anyOtherGlobalVar }){
store.dispatch...
// destructuring approach changes the scope of the function and `this` does not have access to data, computed and e.t.c
}
If you want to access this scope for example this.data, avoid destructuring and access everything through this.
async fetch() {
this.$store...
this.data...
}
In vue 2+ I can easily get the instance of this as a result I can write something like this,
// main.js
app.use(ElMessage)
// home.vue
this.$message({
showClose: true,
message: 'Success Message',
type: 'success',
})
What should I do for vue 3 as,
Inside setup(), this won't be a reference to the current active
instance Since setup() is called before other component options are
resolved, this inside setup() will behave quite differently from this
in other options. This might cause confusions when using setup() along
other Options API. - vue 3 doc.
Using ElMessage directly
ElementPlus supports using ElMessage the same way as $message(), as seen in this example:
import { ElMessage } from 'element-plus'
export default {
setup() {
const open1 = () => {
ElMessage('this is a message.')
}
const open2 = () => {
ElMessage({
message: 'Congrats, this is a success message.',
type: 'success',
})
}
return {
open1,
open2,
}
}
}
Using $message()
Vue 3 provides getCurrentInstance() (an internal API) inside the setup() hook. That instance allows access to global properties (installed from plugins) via appContext.config.globalProperties:
import { getCurrentInstance } from "vue";
export default {
setup() {
const globals = getCurrentInstance().appContext.config.globalProperties;
return {
sayHi() {
globals.$message({ message: "hello world" });
},
};
},
};
demo
Note: Being an internal API, getCurrentInstance() could potentially be removed/renamed in a future release. Use with caution.
Providing a different method where the idea is to set a globally scoped variable to the _component property of the viewmodel/app or component:
pageVM = Vue.createApp({
data: function () {
return {
renderComponent: true,
envInfo: [],
dependencies: [],
userGroups: []
}
},
mounted: function () {
//Vue version 3 made it harder to access the viewmodel's properties.
pageVM_props = pageVM._component;
this.init();
},
I'm new in Vue and would like assistance on how to access and use variables created in Mounted() in my methods.
I have this code
Template
<select class="controls" #change="getCatval()">
Script
mounted() {
var allcards = this.$refs.allcards;
var mixer = mixitup(allcards);
},
methods: {
getCatval() {
var category = event.target.value;
// I want to access mixer here;
}
}
I can't find a solution anywhere besides this example where I could call a method x from mounted() and pass mixer to it then use it inside my getCatval()
Is there an easier way to access those variables?
I will first suggest you to stop using var, and use the latest, let and const to declare variable
You have to first declare a variable in data():
data(){
return {
allcards: "",
mixer: ""
}
}
and then in your mounted():
mounted() {
this.allcards = this.$refs.allcards;
this.mixer = mixitup(this.allcards);
},
methods: {
getCatval() {
let category = event.target.value;
this.mixer
}
}
like Ninth Autumn said : object returned by the data function and props of your components are defined as attributes of the component, like your methods defined in the method attribute of a component, it's in this so you can use it everywhere in your component !
Here an example:
data() {
return {
yourVar: 'hello',
};
},
mounted() { this.sayHello(); },
method: {
sayHello() { console.log(this.yourVar); },
},
Update
you cannot pass any value outside if it's in block scope - Either you need to get it from a common place or set any common value
As I can see, var mixer = mixitup(allcards); is in the end acting as a function which does some operation with allcards passed to it and then returns a value.
1 - Place it to different helper file if mixitup is totally independent and not using any vue props used by your component
In your helper.js
const mixitup = cards => {
// Do some operation with cards
let modifiedCards = 'Hey I get returned by your function'
return modifiedCards
}
export default {
mixitup
}
And then in your vue file just import it and use it is as a method.
In yourVue.vue
import Helpers from '...path../helpers'
const mixitup = Helpers.mixitup
export default {
name: 'YourVue',
data: ...,
computed: ...,
mounted() {
const mixer = mixitup(allcards)
},
methods: {
mixitup, // this will make it as `vue` method and accessible through
this
getCatval() {
var category = event.target.value;
this.mixitup(allcards)
}
}
}
2- Use it as mixins if your mixitup dependent to your vue and have access to vue properties
In your yourVueMixins.js:
export default {
methods: {
mixitup(cards) {
// Do some operation with cards
let modifiedCards = 'Hey I get returned by your function'
return modifiedCards
}
}
}
And import it in your vue file:
import YourVueMixins from '...mixins../YourVueMixins'
const mixitup = Helpers.mixitup
export default {
name: 'YourVue',
mixins: [YourVueMixins] // this will have that function as vue property
data: ...,
computed: ...,
mounted() {
const mixer = this.mixitup(allcards)
},
methods: {
getCatval() {
var category = event.target.value;
this.mixitup(allcards)
}
}
}
Please take a look at this not-working pseudo code:
Vue.component('child', {
props: [],
template: '<div><input v-model="text"></div>',
data: function() {
return {child-text: ""}
}
})
Vue.component('parent', {
template: '<h1> {{text}} </h1>'
data: function() {
return {parent-text: ""}
}
})
What is the most elegant way to fix this code that whenever the user changes the content of input box in child component, then the variable child-text in child component and the variable parent-text in parent component will change automatically? I also want that if the variable child-text and/or parent-text change then the content of input box will change respectively?
I solved this with my own little data store, its a very simple approach but works good enough for me without the necessity to dive into Vuex.
First, I create my data store somewhere before initializing anything else.
window.globalData = new Vue({
data: {
$store: {}
},
});
After that, I add a global Mixin that allows to get and set data to the global storage.
Vue.mixin({
computed: {
$store: {
get: function () { return window.globalData.$data.$store },
set: function (newData) { window.globalData.$data.$store = newData; }
}
}
});
Then, every component can access the data storage by this.$store. You can check a working example here:
https://codesandbox.io/s/62wvro7083