I’m passing a map to a component and then emit back new values and update the map. This triggers the watch on the map, but the old and new values passed are the same.
Is it possible in this case to have a watch that receives old values?
(function() {
const ui = {
setup() {
const map = reactive(new Map([
['width', 800],
['height', 400]
]));
function onCompUpdate(evt) {
console.log(map.get('width'), map.get('height'), evt[0], evt[1]);
map.set('width', Number(evt[0]));
map.set('height', Number(evt[1]));
}
watch(map, (n,o)=>{
console.log(n.get('width'), n.get('height'),
o.get('width'), o.get('height'));
});
return { map, onCompUpdate };
},
};
const vueApp = createApp(ui);
vueApp.component('base-input', {
props: ['some' ], emits: ['comp-update'],
setup(props, { emit }) {
let chars = ref(Array.from(props.some.values()).join(','));
function checkInput(val) {
emit('comp-update', val.split(','));
chars.value = val;
}
return { chars, checkInput };
},
template: `<input type="text" spellcheck="false" :value="chars"
input="checkInput($event.target.value)"/>`
});
vueApp.mount('#vue');
})();
HTML:
<div id="vue">
<base-input :some="map" #comp-update="onCompUpdate($event)"></base-input>
</div>
Fiddle:
https://jsfiddle.net/tfoller/sm28u7r0/35/
It only triggers the watch if the whole Map is replaced. If you want to watch the mutation (adding/removing items), you need to set deep: true like so:
watch(myMap, () => {
// myMap was mutated
}, { deep: true })
Working SFC Playground example
This happens because the references to old and new are the same. Here's one workaround. Instead of watching the reference directly, watch the spreading of the reference, which does change. It has to be done inside a function expression since the spread is not reactive:
watch(() => [...map], (nArray, oArray)=>{
const n = new Map(nArray);
const o = new Map(oArray);
console.log(n.get('width'), n.get('height'), o.get('width'), o.get('height'));
});
Since the spread converts the map to an array, inside the watch you can convert the values back to maps.
Here is your updated fiddle
My own vue component sends http request to receive array of objects, then I store the answer in data property, and it's fine. Now I want to bind this array to v-model, but when user will input something my array is changed too. I want to store the array for later and make it not editable, I just want to bind its value to v-model, not reference to my array. My target is to allow user to reset v-model value to array received from api. I hope you get the point and you will be able to help me.
<draggable v-model="myArray">
<div v-for="element in myArray" :key="element.id">{{element.name}}</div>
</draggable>
<button #click="addElement">New</button>
data() {
return {
myArray: [],
array: []
}
},
methods: {
addElement() {
myArray.push({id:1, name:'something'});
},
getData() {
axios(...)
.then(res => {
this.array = response.data;
});
}
setData() {
this.myArray = this.array;
}
}
Now if user will add new element to myArray it will be also inserted in array
Data must be cloned:
new Vue({
template: '<div>List1:<ul><li v-for="i in array1" :key="i.id">{{i.name}}</li></ul>List2:<ul><li v-for="i in array2" :key="i.id">{{i.name}}</li></ul><button #click="add">Add</button></div>',
data: {
array1: [{id:1, name:'Item1'},{id:2, name:'Item2'}],
array2: []
},
created() {
// clone array
this.array2 = this.array1.map(i => Object.assign({},i))
},
methods: {
add() {
this.array1.push({id:this.array1.length+1, name:'Item'+(this.array1.length+1)})
this.array1[0].name = 'Item1/' + this.array1.length
}
}
}).$mount('div')
<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>
<div></div>
If it is more complex array of objects, then must use some sort of deep-clone.
I solved a similar issue using the JSON parse to make the to-be-copied-array loose dinamic relation with the array-to-be-created. Try the following:
data() {
return {
myArray: [],
array: []
}
},
methods: {
addElement() {
myArray.push({id:1, name:'something'});
},
getData() {
axios(...)
.then(res => {
this.array = response.data;
});
}
setData() {
this.myArray = JSON.parse(JSON.stringify(this.array)); // Here goes the trick
}
}
This way every change on v-model array by the user won't be reflected on myArray since the setData() is called at least once before the user interaton.
Hope it suits you well.
I'm modifying the value of an existing property on an object that is in an array of objects in my Vuex.store. When I update the store, it is not triggering a re-render of my computed property that is accessing the store. If I reset the stored value to an empty array, and then set it again to my new array, it'll trigger the change. But simply updating the property of the array of objects does not trigger a change.
I have tried using Vue.set() like the docs talk about, and that updates the store, but still does not trigger a re-render of the computed property. What am I missing? Using Vue 2.2.4 and Vuex 2.2.0.
//DEBUG: An example of the updated post I'm adding
let myNewScheduledPost = {
id: 1,
name: 'James'
};
this.$store.dispatch('addScheduledPost', post);
//DEBUG: My store
const options = {
state: {
scheduledPosts: [
{ id: 1, name: 'Jimmy'}
],
},
mutations: {
scheduledPosts: (state, scheduledPosts) => {
//This triggers the reactivity/change so my computed property re-renders
//But of course seems the wrong way to do it.
state.scheduledPosts = [];
state.scheduledPosts = scheduledPosts;
//Neither of these two lines triggers my computed property to re-render, even though there is a change in scheduledPosts
state.scheduledPosts = scheduledPosts;
Vue.set(state, 'scheduledPosts', scheduledPosts);
},
},
actions: {
addScheduledPost({ commit, getters }, newScheduledPost) {
let scheduledPosts = getters.scheduledPosts;
const idx = scheduledPosts.findIndex(existingScheduledPost => existingScheduledPost.id === newScheduledPost.id);
//If the post is already in our list, update that post
if (idx > -1) {
scheduledPosts[idx] = newScheduledPost;
} else {
//Otherwise, create a new one
scheduledPosts.push(newScheduledPost);
}
commit('scheduledPosts', scheduledPosts);
//DEBUG: This DOES have the correct updated change - but my component does not see the change/reactivity.
console.log(getters.scheduledPosts);
}
},
getters: {
scheduledPosts: (state) => {
return state.scheduledPosts;
}
}
};
//DEBUG: Inside of my component
computed: {
mySortedPosts()
{
console.log('im being re-rendered!');
return this.$store.getters.scheduledPosts.sort(function() {
//my sorted function
});
}
}
Your problem is if you are wanting to access a portion of the state you don't use a getter https://vuex.vuejs.org/en/state.html.
computed: {
mySortedPosts(){
return this.$store.state.scheduledPosts
}
}
Getters are for computed properties in the store https://vuex.vuejs.org/en/getters.html. So in your case you might create a getter to sort your scheduled posts then name it sortedScheduledPosts and then you can add it to your components computed properties like you are now.
The key thing is your getter needs to have a different name then your state property just like you would in a component.
I'm trying to understand how to properly watch for some prop variation.
I have a parent component (.vue files) that receive data from an ajax call, put the data inside an object and use it to render some child component through a v-for directive, below a simplification of my implementation:
<template>
<div>
<player v-for="(item, key, index) in players"
:item="item"
:index="index"
:key="key"">
</player>
</div>
</template>
... then inside <script> tag:
data(){
return {
players: {}
},
created(){
let self = this;
this.$http.get('../serv/config/player.php').then((response) => {
let pls = response.body;
for (let p in pls) {
self.$set(self.players, p, pls[p]);
}
});
}
item objects are like this:
item:{
prop: value,
someOtherProp: {
nestedProp: nestedValue,
myArray: [{type: "a", num: 1},{type: "b" num: 6} ...]
},
}
Now, inside my child "player" component I'm trying to watch for any Item's property variation and I use:
...
watch:{
'item.someOtherProp'(newVal){
//to work with changes in "myArray"
},
'item.prop'(newVal){
//to work with changes in prop
}
}
It works but it seems a bit tricky to me and I was wondering if this is the right way to do it. My goal is to perform some action every time prop changes or myArray gets new elements or some variation inside existing ones. Any suggestion will be appreciated.
You can use a deep watcher for that:
watch: {
item: {
handler(val){
// do stuff
},
deep: true
}
}
This will now detect any changes to the objects in the item array and additions to the array itself (when used with Vue.set). Here's a JSFiddle: http://jsfiddle.net/je2rw3rs/
EDIT
If you don't want to watch for every change on the top level object, and just want a less awkward syntax for watching nested objects directly, you can simply watch a computed instead:
var vm = new Vue({
el: '#app',
computed: {
foo() {
return this.item.foo;
}
},
watch: {
foo() {
console.log('Foo Changed!');
}
},
data: {
item: {
foo: 'foo'
}
}
})
Here's the JSFiddle: http://jsfiddle.net/oa07r5fw/
Another good approach and one that is a bit more elegant is as follows:
watch:{
'item.someOtherProp': function (newVal, oldVal){
//to work with changes in someOtherProp
},
'item.prop': function(newVal, oldVal){
//to work with changes in prop
}
}
(I learned this approach from #peerbolte in the comment here)
VueJs deep watch in child objects
new Vue({
el: "#myElement",
data: {
entity: {
properties: []
}
},
watch: {
'entity.properties': {
handler: function (after, before) {
// Changes detected. Do work...
},
deep: true
}
}
});
Personally I prefer this clean implementation:
watch: {
myVariable: {
handler(newVal, oldVal){ // here having access to the new and old value
// do stuff
console.log(newVal, oldVal);
},
deep: true,
/*
Also very important the immediate in case you need it,
the callback will be called immediately after the start
of the observation
*/
immediate: true
}
}
How if you want to watch a property for a while and then to un-watch it?
Or to watch a library child component property?
You can use the "dynamic watcher":
this.$watch(
'object.property', //what you want to watch
(newVal, oldVal) => {
//execute your code here
}
)
The $watch returns an unwatch function which will stop watching if it is called.
var unwatch = vm.$watch('a', cb)
// later, teardown the watcher
unwatch()
Also you can use the deep option:
this.$watch(
'someObject', () => {
//execute your code here
},
{ deep: true }
)
Please make sure to take a look to docs
Another way to add that I used to 'hack' this solution was to do this:
I set up a seperate computed value that would simply return the nested object value.
data : function(){
return {
countries : {
UnitedStates : {
value: "hello world";
}.
},
};
},
computed : {
helperName : function(){
return this.countries.UnitedStates.value;
},
},
watch : {
helperName : function(newVal, oldVal){
// do this...
}
}
Tracking individual changed items in a list
If you want to watch all items in a list and know which item in the list changed, you can set up custom watchers on every item separately, like so:
var vm = new Vue({
data: {
list: [
{name: 'obj1 to watch'},
{name: 'obj2 to watch'},
],
},
methods: {
handleChange (newVal, oldVal) {
// Handle changes here!
// NOTE: For mutated objects, newVal and oldVal will be identical.
console.log(newVal);
},
},
created () {
this.list.forEach((val) => {
this.$watch(() => val, this.handleChange, {deep: true});
});
},
});
If your list isn't populated straight away (like in the original question), you can move the logic out of created to wherever needed, e.g. inside the .then() block.
Watching a changing list
If your list itself updates to have new or removed items, I've developed a useful pattern that "shallow" watches the list itself, and dynamically watches/unwatches items as the list changes:
// NOTE: This example uses Lodash (_.differenceBy and _.pull) to compare lists
// and remove list items. The same result could be achieved with lots of
// list.indexOf(...) if you need to avoid external libraries.
var vm = new Vue({
data: {
list: [
{name: 'obj1 to watch'},
{name: 'obj2 to watch'},
],
watchTracker: [],
},
methods: {
handleChange (newVal, oldVal) {
// Handle changes here!
console.log(newVal);
},
updateWatchers () {
// Helper function for comparing list items to the "watchTracker".
const getItem = (val) => val.item || val;
// Items that aren't already watched: watch and add to watched list.
_.differenceBy(this.list, this.watchTracker, getItem).forEach((item) => {
const unwatch = this.$watch(() => item, this.handleChange, {deep: true});
this.watchTracker.push({ item: item, unwatch: unwatch });
// Uncomment below if adding a new item to the list should count as a "change".
// this.handleChange(item);
});
// Items that no longer exist: unwatch and remove from the watched list.
_.differenceBy(this.watchTracker, this.list, getItem).forEach((watchObj) => {
watchObj.unwatch();
_.pull(this.watchTracker, watchObj);
// Optionally add any further cleanup in here for when items are removed.
});
},
},
watch: {
list () {
return this.updateWatchers();
},
},
created () {
return this.updateWatchers();
},
});
I've found it works this way too:
watch: {
"details.position"(newValue, oldValue) {
console.log("changes here")
}
},
data() {
return {
details: {
position: ""
}
}
}
Not seeing it mentioned here, but also possible to use the vue-property-decorator pattern if you are extending your Vue class.
import { Watch, Vue } from 'vue-property-decorator';
export default class SomeClass extends Vue {
...
#Watch('item.someOtherProp')
someOtherPropChange(newVal, oldVal) {
// do something
}
...
}
My problem with the accepted answer of using deep: true, is that when deep-watching an array, I can't easily identify which element of the array contains the change. The only clear solution I've found is this answer, which explains how to make a component so you can watch each array element individually.
None of the answer for me was working. Actually if you want to watch on nested data with Components being called multiple times. So they are called with different props to identify them.
For example <MyComponent chart="chart1"/> <MyComponent chart="chart2"/>
My workaround is to create an addionnal vuex state variable, that I manually update to point to the property that was last updated.
Here is a Vuex.ts implementation example:
export default new Vuex.Store({
state: {
hovEpacTduList: {}, // a json of arrays to be shared by different components,
// for example hovEpacTduList["chart1"]=[2,6,9]
hovEpacTduListChangeForChart: "chart1" // to watch for latest update,
// here to access "chart1" update
},
mutations: {
setHovEpacTduList: (state, payload) => {
state.hovEpacTduListChangeForChart = payload.chart // we will watch hovEpacTduListChangeForChart
state.hovEpacTduList[payload.chart] = payload.list // instead of hovEpacTduList, which vuex cannot watch
},
}
On any Component function to update the store:
const payload = {chart:"chart1", list: [4,6,3]}
this.$store.commit('setHovEpacTduList', payload);
Now on any Component to get the update:
computed: {
hovEpacTduListChangeForChart() {
return this.$store.state.hovEpacTduListChangeForChart;
}
},
watch: {
hovEpacTduListChangeForChart(chart) {
if (chart === this.chart) // the component was created with chart as a prop <MyComponent chart="chart1"/>
console.log("Update! for", chart, this.$store.state.hovEpacTduList[chart]);
},
},
I used deep:true, but found the old and new value in the watched function was the same always. As an alternative to previous solutions I tried this, which will check any change in the whole object by transforming it to a string:
created() {
this.$watch(
() => JSON.stringify(this.object),
(newValue, oldValue) => {
//do your stuff
}
);
},
For anyone looking for Vue 3
import { watch } from 'vue';
...
...
watch(
() => yourNestedObject, // first param, your object
(currValue, prevValue) => { // second param, watcher callback
console.log(currValue, prevValue);
},
{ deep: true } // third param, for deep checking
);
You can refer to the documentation here: https://v3.vuejs.org/guide/reactivity-computed-watchers.html#watch
Here's a way to write watchers for nested properties:
new Vue({
...allYourOtherStuff,
watch: {
['foo.bar'](newValue, oldValue) {
// Do stuff here
}
}
});
You can even use this syntax for asynchronous watchers:
new Vue({
...allYourOtherStuff,
watch: {
async ['foo.bar'](newValue, oldValue) {
// Do stuff here
}
}
});
https://vuejs.org/guide/essentials/watchers.html#deep-watchers
export default {
watch: {
someObject: {
handler(newValue, oldValue) {
// Note: `newValue` will be equal to `oldValue` here
// on nested mutations as long as the object itself
// hasn't been replaced.
},
deep: true
}
}
}
I got a vue object like this:
var vm = new Vue({
el: '#app',
data: {
items: [],
index: 0
},
});
Inside items array i will push items like:
item1 = {
a: 1,
b: 'type',
c: '3.556'
}
...
itemN = {
a: n,
b: 'type',
c: '5.226'
}
then i will update one of the item's "c" property and i would like to set up a watcher that warn me as soon as one of this property changes.
EDIT: i also want to know witch item has changed
You can use deep watch, but... it does not provide ease way to determine which item has changed.
...
watch: {
items: {
handler: function (val, oldVal) {
},
deep: true
}
}
...
One of possible workarounds is mentioned in this answer,
idea behind this solution is to wrap each item in component and listen to event from component.
You can also store cloned items array and update that clone in watch handler, you can use that clone to filter item that has changed.