I have this code and the goal from it is to update a data sticky to true if the scroll position is > than 0
export default {
components: {
},
data() {
return {
menuVisible: false,
sticky: false,
}
},
mounted() {
this.checkScroll()
},
methods: {
checkScroll() {
document.querySelector('body').onscroll = function() {
console.log(window.pageYOffset > 0)
this.sticky = window.pageYOffset > 0
}
},
},
}
the problem is that even that i see the true console logged, the data is allways false ( as the initial value )
Any idea why is not updating it?
That's because of the callback you're passing into your scroll listener. In your callback this is not the context of the vue component. I think its the body actually. You'll need to use an arrow function or pass the vue instance into the callback as an argument. Arrow function is easiest. An arrow function retains the context where it was defined rather than inheriting the context of the object that calls it. Here is a good post/answer about the difference between normal and arrow functions.
document.querySelector('body').onscroll = () => {
console.log(window.pageYOffset > 0)
this.sticky = window.pageYOffset > 0
}
Related
I have this vue component:
export default {
data: function() {
return {
editor: new Editor({
//some options
}),
}
},
computed: {
doc(){ // <--------------------- take attention on this computed property
return this.editor ? this.editor.view.state.doc : null;
},
},
watch: {
doc: {
handler: function(val, OldVal){
// call some this.editor methods
},
deep: true,
immediate: true,
},
},
}
Will computed property doc be dependent on a data property editor if I use this.editor only for checking if it is defined and not use it for assigning it to the doc? I mean, If I will change this.editor will doc be changed? Also, I have watcher on doc so I need to know if I will cause an infinite loop.
In the doc property computation, you use:
the editor property (at the beginning of your ternary, this.editor ? ...)
if editor exists, the editor.view.state.doc property
So the computation of doc will be registered by Vue reactivity system as an effect related to the properties editor and (provided that editor exists) to editor.view.state.doc. In other words, the doc property will be reevaluated each time one of these two properties changes.
=> to reply to the initial question, doc will indeed depend on editor.
This can be toned though, because by 'property change', we mean:
for properties of primitive types, being reassigned with a different value
for objects, having a new reference
So, in our case, if editor, which is an object, is just mutated, and that this mutation does not concern it's property editor.view.state.doc, then doc will not be reevaluated. Here are few examples:
this.editor = { ... } // doc will be reevaluated
this.editor.name = ' ... ' // doc will NOT be reevaluated
this.editor.view.state.doc = { ... } // doc will be reevaluated
If you want to understand this under the hood, I would recommand these resources (for Vue 3):
the reactivity course on Vue Mastery (free)
this great talk and demo (building a simple Vue-like reactivity system)
About the inifinite loop, the doc watcher handler will be executed only:
if doc is reassigned with a different value
in the case where docis an object, if doc is mutated (since you applied the deep option to the doc watcher)
The only possibility to trigger an infinite loop would be to, in the doc watcher handler, mutate or give a new value to doc (or editor.view.state.doc). For example (cf #Darius answer):
watch: {
doc: {
handler: function(val, OldVal){
// we give a new ref each time this handler is executed
// so this will trigger an infinite loop
this.editor.view.state.doc = {}
},
// ...
},
}
=> to reply to the second question, apart from these edge cases, your code won't trigger a loop. For example:
watch: {
doc: {
handler: function(val, OldVal){
// even if we mutate the editor object, this will NOT trigger a loop
this.editor.docsList = []
},
// ...
},
}
Changing editor variable should work, but changing Editor content may not, as it depends on Editor class and how it respects reactivity.
For example:
export default {
data: function() {
return {
editor: {text: '' }
}
}
}
...
this.editor.text = 'Text' // works
this.editor.text = {param: ''} // works
this.editor.text.param = 'value' // works
this.editor.param = {} // does't work, as creation of new property is not observable
If editor observer works and you are changing editor property in observer, which 'reinitializes' internal structures, it may lead to infinite loop:
var Editor = function() {
this.document = {}
this.change = () => { this.document = {} }
}
var data = new Vue({
data: () => ({
editor: new Editor(),
check: 0
}),
watch: {
editor: {
handler() {
this.check++
console.log('Changed')
if (this.check < 5)
this.editor.change()
else
console.log('Infinite loop!')
},
deep: true,
immediate: true
}
}
})
data.editor.change()
<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.min.js"></script>
In such case, extra checking is necessary before making the change.
I want this select multiple to pre-select one option, and not be able to deselect all options.
Whenever the last selected option is deselected it should be reselected. In other words when the user tries to deselect the last selected option it should visually not be deselected.
<template>
<b-select
if="Object.keys(doc).length !== 0 /* wait until firebase has loaded */"
:options="computedOptions"
v-model="model"
multiple
#input="onChange"
/>
</template>
<script>
//import Vue from 'vue'
import { fb } from "../fbconf";
export default {
name: "MyMultiSelect",
props: {
doc: Object, // firestore document
},
data() {
return {
options: []
};
},
firestore() {
var options = fb.db.collection("options");
return {
options: options
};
},
computed: {
computedOptions: function() {
return this.options.map(function(option) {
return {
text: option.name,
value: option.id
};
});
},
// to make sure mySelectedOptions is an array, before this.doc is loaded
// I use the following custom model
// because not using 'get' below causes a warning:
// [Vue warn]: <select multiple v-model="localValue"> expects an Array value for its binding, but got Undefined
model: {
get: function() {
if (!this.doc.hasOwnProperty('mySelectedOptions')) return []; // empty array before this.doc is loaded
else return this.doc['mySelectedOptions'];
},
set: function(newValue) {
// here I can prevent the empty array from being stored
// but visually the user can deselect all options, which is bad UX
//if (Array.isArray(newValue) && newValue.length > 0) this.doc['mySelectedOptions'] = newValue;
}
},
},
methods: {
onChange: function(newValue){
// I can manually store the array as I want here
// but I cannot in any way prevent the user from deselecting all options
if (Array.isArray(newValue) && newValue.length > 0) this.doc['mySelectedOptions'] = newValue;
else {
// none of these reselects the last selected option
var oldValue = this.doc['mySelectedOptions'];
this.doc['mySelectedOptions'] = this.doc['mySelectedOptions'];
//this.$forceUpdate();
//this.$emit("change", newValue);
//Vue.set(this.doc, 'mySelectedOptions', this.doc['mySelectedOptions']);
}
}
}
};
</script>
You could add watcher and when length becomes 0 just add previous value.
watch: {
model(val, oldVal) {
if(val.length == 0 && oldVal.length > 0) {
// take only one item in case there's clear button or etc.
this.model = [oldval[0]];
}
}
}
I am developing a project using Vue JS and I need to watch the props changes and call it inside a <span>.
I have used watch() and it shows that the props values are assigned.
But when I call it inside the <span> the value is not showing.
props: ['verifyText', 'verifyValue', 'profileId', 'logged', 'verifyType', 'status'],
watch: {
verifyText: function () { // watch it
this.verify_text = this.verifyText;
},
verifyValue: function () {
this.verify_value = this.verifyValue;
},
verifyType: function () {
this.verify_type = this.verifyType;
}
},
data() {
return {
verify_type: this.verifyType,
verify_text: this.verifyText,
verify_value: this.verifyValue,
}
},
//using inside span
<span>{{verify_text}}</span>
Receive and insert new data that changes from 'watch'
Try this.
props: ['verifyText', 'verifyValue', 'profileId', 'logged', 'verifyType', 'status'],
watch: {
verifyText: function (new_value) {
this.verify_text = new_value;
}
},
data() {
return {
verify_text: this.verifyText,
}
},
//using inside span
<span>{{verify_text}}</span>
I solved this issue by watching the verify_text in the parent component.
'verify_text': function (value) {
this.verify_text = value;
},
Same for the verify_type and verify_value
Thank you all for replying.
As the title says, I'm trying to change the value of a prop/data in a component, but the trigger is being fired from outside the component, from something that has nothing to do with Vuejs.
Currently I trying to use a Simple State Manager, based on the docs from here, like so:
var store = {
debug: true,
state: {
progress: 23
},
setProgress (uff) {
if (this.debug) console.log(uff)
this.state.progress = uff
}
}
The documentation leads me to believe that if the value of progress is mutated, the value of my Vue instance would also change if I link them accordingly. But this doesn't work in a component (my guess would be it's cause it's a function).
This is part of my component:
Vue.component('transcoding', {
data () {
return {
progress: store.state.progress
}
},
template: `
<v-progress-circular
:size="130"
:width="25"
:value="progress"
color="teal"
>
{{progress}}
</v-progress-circular>
`
})
So, when I trigger a store.setProgress(value), nothing happens. The log messages do happen, but the state isn't updated in the component.
This is the script that's currently triggering the state change:
App.cable.subscriptions.create(
{ channel: "ProgressChannel", room: "2" },
{ received: function() {
store.setProgress(arguments[0])
}}
)
It's an ActionCable websocket in Ruby on Rails. The trigger works perfectly, but I just cannot make the connection between the state change and the component.
I tried loading this script in the mounted() event for the component, thinking I could reference the value like this:
Vue.component('transcoding', {
data () {
return {
progress: 0
}
},
template: `
<v-progress-circular
:size="130"
:width="25"
:value="progress"
color="teal"
>
{{progress}}
</v-progress-circular>
`,
methods: {
setProgress: function(uff) {
this.progress = uff
}
},
mounted() {
App.cable.subscriptions.create(
{ channel: "ProgressChannel", room: "2" },
{ received: function() {
this.setProgress(arguments[0])
}}
)
}
})
But this gives me an error saying that this.setProgress is not a function, which is obvious since I'm calling it within the create method of App.cable.subscriptions.
How can I make this work? I realize I'm mixing things with my question, but I wanted to illustrate what my goal is. I simply want to know how to make the component's progress data to update, either from the outside, or from the component itself if I can make it find the function.
You are initializing your data item to the value from the store:
data () {
return {
progress: store.state.progress
}
}
Changes to the store will not propagate to your data item. You could eliminate the data item and just use store.state.progress where you need it, or you could create an computed that returns its value if you want a local single-name handle for it.
I have a component to display names. I need to calculate number of letters for each name.
I added nameLength as computed property but vuejs doesn't determine this property in loop.
var listing = Vue.extend({
template: '#users-template',
data: function () {
return {
query: '',
list: [],
user: '',
}
},
computed: {
computedList: function () {
var vm = this;
return this.list.filter(function (item) {
return item.toLowerCase().indexOf(vm.query.toLowerCase()) !== -1
})
},
nameLength: function () {
return this.length; //calculate length of current item
}
},
created: function () {
this.loadItems();
},
methods: {
loadItems: function () {
this.list = ['mike','arnold','tony']
},
}
});
http://jsfiddle.net/apokjqxx/22/
So result expected
mike-4
arnold-6
tony-4
it seems there is some misunderstanding about computed property.
I have created fork from you fiddle, it will work as you needed.
http://jsfiddle.net/6vhjq11v/5/
nameLength: function () {
return this.length; //calculate length of current item
}
in comment it shows that "calculate length of current item"
but js cant get the concept of current item
this.length
this will execute length on Vue component it self not on that value.
computed property work on other property of instance and return value.
but here you are not specifying anything to it and used this so it wont able to use any property.
if you need any more info please comment.