I have a loop that outputs checkboxes:
<div v-for="(value, key) in optionsObject" :key="key">
In computed I check whether the prop options is an object or an array (if array I make they key from the array values)...
computed: {
optionsObject() {
return _.isPlainObject(this.options) ? this.options : _.zipObject(this.options, this.options);
}
}
But everytime the checkbox is changed, it runs the computed optionsObject again. Is there anyway to prevent this?
That is how a computed property in Vue works. It refresh when a property that it depends on changes. For performances this is a huge advantage compared to a method(), as noted in the docs:
Instead of a computed property, we can define the same function as a
method. For the end result, the two approaches are indeed exactly the
same. However, the difference is that computed properties are cached
based on their reactive dependencies. A computed property will only
re-evaluate when some of its reactive dependencies have changed.
Related
I'm trying to create a simple component whose focus is to display an element in an array, but I'm having issues with Vue's philosophy.
As you may know, if a mutation on a prop is triggered, Vue goes crazy because it doesn't want you to update the value of a prop. You should probably use a store, or emit an event.
The issue is: that since I'm adding functionalities to my codebase (for instance the possibility to start again when I reach the last element of the array), it would be wrong to have an upper component be responsible for this management, as it would be wrong to ask an upper component to change their variable, given that my component is supposed to manage the array, so an emit would be a bad solution.
In the same way, given that I'm making a generic component that can be used multiple times on a page, it would be incorrect to bind it to a store.
EDIT: the reason why the prop needs to be updated is that the component is basically acting as a <select>
Am I missing an obvious way to set this up?
To give an example of my end goal, I'm aiming for a component looking like the one in the picture below, and I think a 2 way bind like in v-model would be more appropriate than having to set an #change just to say to update the value of the passed prop.
If you have a prop the correct way to update the value is with a sync, as in the following example
Parent:
<my-component :title.sync="myTitle"></my-component>
Child:
this.$emit("update:title", this.newValue)
Here is a very good article talking about the sync method.
By the other hand you can alter a Vuex state variable by calling a Vuex mutation when you change the value:
computed: {
title: {
// getter
get() {
return this.$store.state.title
},
// setter
set(newValue) {
this.setTitle(newValue) // Requires mutation import, see the methods section.
// Or without import:
this.$store.commit('setTitle', newValue);
}
}
},
methods: {
...mapMutations("global", ["setTitle"]) // It is important to import the mutation called in the computed section
}
In this StackOverflow question they talk about changing state from computed hook in Vue. I hope it works for you.
I have problem understanding why THE SAME mutation fails to refresh data displayed in components (although it does change underlying vuex store data!) if it is called from one of the components, but it does refresh the data if called from another component?
I am updating Filter objects stored in store this way: state.report.filters[], where filters is array of Filter objects.
const state = {
report: {
filters: [], // array of Filter objects
...
}
}
My mutation looks for a filter in the array and substitutes the whole Filter object.
const mutations = {
setFilter: (state, newFilterValue) => {
let changedFilter = state.report.filters.find(filter => {
return filter.fieldName === newFilterValue.fieldName;
});
changedFilter = newFilterValue;
}
}
The mutation is called from a method of Filter class defined like this (separate module):
import { store } from './store';
export class Filter {
constructor ({
...
} = {}) {
this.operators = []; // Array of Operator objects
this.value = []; // Array of values - in this case Dates
};
updateOperator (operatorName) { // this mutation refreshes components when executed
this.operator[0] = new Operator(operatorName);
store.commit('setFilter', this); // whole object passed to the mutation
};
updateValue (newValue) { // this mutation changes store value, but fails to refresh components
this.value[0] = newValue; // newValue is a Date
store.commit('setFilter', this);
};
};
The app displays data in rows (each Filter has a separate row), each row contains cells, of which one contains components dedicated to Filter's value and Operator. These dedicated components receive as props callback functions which are methods of the Filter object. They execute the callback functions when a new value is entered passing the value to the Filter which then updates a relevant property and calls the mutation passing in both cases the whole Filter object as payload.
// TABLE CELL COMPONENT displaying filter value and operator
<template>
<td>
<operator-component
:iconName="proppedFilterObject.operator.iconName"
:callback="proppedFilterObject.updateOperator.bind(proppedFilterObject)"
></operator-component>
<value-component
:date="proppedFilterObject.value[0]"
:callback="proppedFilterObject.updateValue.bind(proppedFilterObject)"
></value-component>
</td>
</template>
<script>
export default {
props: ['proppedFilterObject'] // whole filter object
};
</script>
// OPERATOR COMPONENT
<template>
<div #click.stop="chooseOperator">
{{ iconName }} // some operator value display
</div>
</template>
<script>
export default {
methods: {
chooseOperator () {
const modal = new ChooseOperatorModal({
callback: this.callback // this displays another modal for receiving data. The modal calls the callback.
});
},
},
props: ['callback', 'iconName']
};
</script>
// VALUE COMPONENT
<template>
<date-picker v-model="computedDate"> // THIRD PARTY COMPONENT
</date-picker>
{{ date }} // additional display to verify if there's a problem within 'date-picker'
</template>
<script>
import DatePicker from 'vue2-datepicker'; // THIRD PARTY COMPONENT
export default {
components: { DatePicker },
computed: {
computedDate: {
get: function () {
return this.date;
},
set: function (newValue) {
this.callback(newValue);
}
}
},
props: ['callback', 'date']
};
</script>
So, if eg. I enter new operator value from Operator component, everything refreshes. When I enter a new value in the value component, the mutation is executed and store value changed, but displayed data are not refreshed. However, if afterwards I change an operator all the components will refresh and value will get displayed. Even if I change operator in a different Filter object(!). Ie:
a) Change in report.filters[0].value - display not refreshed, but...
b) then change report.filters[1].operator - both report.filters[1].operator AND PREVIOUSLY CHANGED report.filters[0].value get refreshed(?!).
What can be a reason of such behaviour? Where to look for the problem?
Some additional remarks:
1) I am using a third party component "vue2-date-picker" for date choice and display. However it does not seem to be responsible for the problem, as if I try to display the new value just in {{ }} notation it behaves the same way. I have used the date picker in other components and there it functions correctly as well.
2) In the code samples I left out most imports/exports and other seemingly irrelevant elements to keep the question reasonably short.
There are a lot of problems with the code and several of them are contributing to the problems you're seeing. A full, thorough answer that addresses all of these problems would be ridiculously long so instead I will skim through them without going into huge amounts of detail. You will need to do some further reading and experimentation to understand each of these topics properly.
Let's start with this line in the mutation:
changedFilter = newFilterValue;
This line assigns a new value to the local variable changedFilter. That's all. As it's the last line of the mutation the net result is that it doesn't really do anything.
Presumably your intent was to update the array state.report.filters, replacing the old entry with a new entry. However, just updating a local variable isn't going to do that.
At this point you may be wondering 'If that doesn't do anything, then why is the state in my store changing?'. I'll come to that in a moment but first let me prove to you that your existing code does nothing.
Try removing the code inside setFilter completely. Just leave an empty function. Then try clicking around in the UI just like you did before. You'll find that the store state updates just the same as it did before, even though you've removed the code to update the array.
The correct way to implement that mutation would be to use findIndex to find the relevant index and then use either Vue.set or the array's splice method to update the array accordingly. That will change the item in the array. However...
This brings us back to the earlier question. Why is the state updating if the mutation does nothing?
This is because you're using the same object in multiple places. The Filter object held in the array is the same object that your UI is editing. There are no copies being taken, there is just a single object. So when you change the properties of that object inside updateOperator or updateValue this will immediately be reflected inside the store. Calling the setFilter mutation is just asking the store to replace an object with itself.
There's nothing specific to Vue about this. This is just the standard behaviour of reference types in JavaScript. It is also common with many other programming languages that don't directly expose pointers. It can be useful to learn a little about how pointers work in other languages as it will give you a better initial mental model before attempting to understand how reference types behave in JavaScript. Understanding the difference between 'by value' and 'by reference' may also be a useful starting point.
The next topic to cover is reactivity, which very much is a Vue topic.
Specifically, there are certain changes that Vue can't detect. These are usually referred to as the reactivity caveats. You can find more about them in the official documentation:
https://v2.vuejs.org/v2/guide/reactivity.html#Change-Detection-Caveats
https://v2.vuejs.org/v2/guide/list.html#Caveats
There are at least two lines in your code that violate these rules:
this.operator[0] = new Operator(operatorName);
and
this.value[0] = newValue;
You can't set array entries directly by index. The array will update but it won't trigger any reactive dependencies within Vue. Instead you need to use either Vue.set or one of the array methods, e.g. push, pop, splice, etc.. In this example you could use splice.
e.g. Using Vue.set:
Vue.set(this.value, 0, newValue);
e.g. Using splice:
this.value.splice(0, 0, newValue);
Why does all of this matters?
Well Vue will only re-render a component if its reactive dependencies have changed. They are very similar to computed properties in that regard. Here's how it works...
Vue compiles the template down to a function. That function is referred to as the render function. When rendering a component Vue calls the render function and that function returns a description of how to render the component. Any reactive properties that are touched while that function is running will be recorded as dependencies. If, at some point in the future, the value of one of those reactive properties changes then Vue will rerun the render function to generate a new rendering of that component.
There are two key points to take out of this description:
If you fall foul of one of the reactivity caveats then Vue won't know the dependency has changed, so it won't re-render the component.
The render function runs as a whole. It doesn't just target a small chunk of the template, it always runs the whole thing.
So if you change a dependency in a non-reactive way (i.e. one of the caveats) it won't trigger a rendering update. But if you subsequently update a dependency properly, Vue will detect that and will rerun the render function. When it runs it will run the whole thing, so any new values will be picked up, even if they weren't detected when they changed.
It isn't immediately clear to me which rendering dependency is causing your component to re-render. However, it only needs one of them to change in a detectable manner. Any other changes will then get pulled in incidentally when the render function runs and reads their current values.
That covers why your code isn't working. However, I would also worry about your decision to introduce a Filter class. I understand how that may be appealing if you've come from some other OO environment but it isn't typically how Vue is used. It is possible to make it work but you will need a good understanding of both JavaScript reference types and the Vue reactivity system to avoid falling through the cracks. There is no reason why using a specific class to hold your data can't be made to work but in practice it usually ends up being less maintainable than not using such a class. A more typical Vue approach would be to use simple, anonymous objects/arrays to hold the data and then for the data owner (either a component or store module) to be responsible for making any mutations to that data. Events are used to pass changes up the component hierarchy rather than callback props.
Ultimately you will need to judge whether the Filter class is justified but it is probably not what future maintainers of your code will be expecting.
My Vue:
new Vue({
data: {
...
},
computed: {
peaksAndEstimations: {
get: function () { ... }
set: function () { ... }
I can't receive new values iterating computed variable:
<tr v-for="(peak, index) in peaksAndEstimations">
<td>
<input v-model="peak.estimation.name">
</td>
set() method doesn't invoke on changes in input field. All works with normal variables from data section.
What am I doing wrong?
Found another post about it: here
What am I doing wrong?
You have a computed array with a setter. The setter expects to receive a new value for the computed – an array in your case. Your input is bound to a member of a member of an element of that array. You can't expect Vue to compose a modified array and pass that to your array setter.
The input will modify that member of a member of the actual element that your getter put into the computed array. Whether you can make use of that modification depends on how you composed the array.
If you want to modify individual elements, you probably want a real array and not a computed one. What objective are you working toward with this?
Some workarounds from https://www.reddit.com/r/vuejs/comments/741hwk/vfor_computed_value/
Use a computed property in the parent which maps over the original Array and produces a new Array of the desired format.
Or add a new component for rendering each item in the array. e.g. if the parent is then make a new child component which contains the computed properties that you want each child to have access to.
Or you're also allowed to call methods in your prop expression so you could add a method on the parent component that returns the desired new value. This is probably less performant since method calls don't get cached like computed properties but i don't see why it wouldn't work.
Is there a difference between the following? I've seen examples doing both and am unsure why you would choose one over the other.
Vue.component('test', {
data() {
return { myDataA: 10 };
}
//vs
created() {
this.myDataB = 10;
}
}
Variables set in created() on this will not be reactive. In order for them to be reactive, you must define them in the object returned by data().
Example (note how the text does not change in the output):
https://jsfiddle.net/oyf4quyL/
in a component, there are three places where you can define you data:
data properties
computed properties
props
the created property is lifecycle hook in Vue. what this means, is that the Vue will run this function when the component is created. there are also other lifecycle hooks in Vue you can use, like mounted or beforeMount or beforeCreate and etc.
now with this in mind, let's answer your question.
when you define myDataA in data property, Vue will automatically create some "watchers" for this data property, so anytime that you set a new value to myDataA, anywhere that is using it, will be called again. but when you define a property directly on Vue instance (this), you will lose this "watchers" feature. (which by the way is just some getters and setters!)
so as i said, the best way and the correct way to define a data property is on any of the three places that i mentioned, based on your need. (because each of them has different use-cases that the others).
I have a computed property - playerId that is referencing an external object that is not updating.
For example:
var player = require('players');
computed: {
playerId: function() {
return player.id
}
}
If I run this call in a click event it outputs the correct ID. However when this gets updated - computed on its own doesn't update. How do I get this to work? Or am I going about this incorrectly?
Computed Property in Vue.js does not get reactive with the data which doesn't have any reactive dependecy. For example, the code below would not be updated in each time, because Date.now() has no reactive dependency. The result of this computed value gets cached and it always returns the same value as the one returned at the first time.
computed: {
now: function () {
return Date.now()
}
}
Then, you probably would like to know how to make your external object reactive. The point is, you better put your object into data section in order to track the change of it with Vue's internal watcher. If your computed property has even one a reactive dependency such referencing data or calling method, it is notified every time the dependency get updated and the content returned from the computed property is going to be updated as well.
https://v2.vuejs.org/v2/guide/computed.html