Develop Reference

Vue.js - watch particular properties of the object and load data on change

I have Vue component with prop named product, it is an object with a bunch of properties. And it changes often.
export default {
props: {
product: {
type: Object,
default: () => {},
},
},
watch: {
'product.p1'() {
this.loadData()
},
'product.p2'() {
this.loadData()
},
},
methods: {
loadData() {
doApiRequest(this.product.p1, this.product.p2)
}
},
}
The component should load new data when only properties p1 and p2 of product are changed.
The one approach is to watch the whole product and load data when it is changed. But it produces unnecessary requests because p1 and p2 may not have changed.
Another idea is to watch product.p1 and product.p2, and call the same function to load data in each watcher.
But it may happen that both p1 and p2 changed in the new version of the product, it would trigger 2 calls.
Will it be a good solution to use a debounced function for data load?
Or rather use single watcher for the whole product and compare new p1 and p2 stringified with their old stringified versions to determine if data loading should be triggered?

There are several approaches to this, each with pros and cons.
One simple approach I do is to use a watch function that accesses each of the properties you want to watch and then returns a new empty object. Vue knows product.p1 and product.p2 were accessed in the watch function, so it will re-execute it any time either of those properties change. Then, by returning a new empty object instance from the watch function, Vue will trigger the watch handler because the watch function returned a new value (and thus what is being watched "changed").
created() {
this.$watch(() => {
// Touch the properties we want to watch
this.product.p1;
this.product.p2;
// Return a new value so Vue calls the handler when
// this function is re-executed
return {};
}, () => {
// p1 or p2 changed
})
}
Pros:
You don't have to stringify anything.
You don't have to debounce the watch handler function.
Cons:
You can't track the previous values of p1 and p2.
Take care if this.product could ever be null/undefined.
It will always trigger when p1 or p2 are changed; even if p1 and p2 are set back to their previous values before the next micro task (i.e. $nextTick()); but this is unlikely to be a problem in most cases.
You need to use this.$watch(). If you want to use the watch option instead then you need to watch a computed property.
Some of these cons apply to other approaches anyway.
A more compact version would be:
this.$watch(
() => (this.product.p1, this.product.p2, {}),
() => {
// changed
}
})

As some of other developers said you can use computed properties to monitor the changing of product.p1 or product.p2 or both of them and then calling loadData() method only once in each case. Here is the code of a hypothetical product.vue component:
<template>
<div>
this is product compo
</div>
</template>
<script>
export default {
name: "product",
watch: {
p1p2: function(newVal, oldVal) {
this.loadData();
}
},
props: {
productProp: {
type: Object,
default: () => {},
},
},
computed: {
p1p2: function() {
return this.productProp.p1 + this.productProp.p2;
}
},
methods: {
loadData() {
console.log("load data method");
}
},
}
</script>
I renamed the prop that it received to productProp and watched for a computed property called p1p2 in that. I supposed that the values of data are in String format (but if they are not you could convert them). Actually p1p2 is the concatenation of productProp.p1 and productProp.p2. So changing one or both of them could fire the loadData() method. Here is the code of a parent component that passes data to product.vue:
<template>
<section>
<product :productProp = "dataObj"></product>
<div class="d-flex justify-space-between mt-4">
<v-btn #click="changeP1()">change p1</v-btn>
<v-btn #click="changeP2()">change p2</v-btn>
<v-btn #click="changeBoth()">change both</v-btn>
<v-btn #click="changeOthers()">change others</v-btn>
</div>
</section>
</template>
<script>
import product from "../components/product";
export default {
name: 'parentCompo',
data () {
return {
dataObj: {
p1: "name1",
p2: "name2",
p3: "name3",
p4: "name4"
}
}
},
components: {
product
},
methods: {
changeP1: function() {
if (this.dataObj.p1 == "name1") {
this.dataObj.p1 = "product1"
} else {
this.dataObj.p1 = "name1"
}
},
changeP2: function() {
if (this.dataObj.p2 == "name2") {
this.dataObj.p2 = "product2"
} else {
this.dataObj.p2 = "name2"
}
},
changeBoth: function() {
if (this.dataObj.p2 == "name2") {
this.dataObj.p2 = "product2"
} else {
this.dataObj.p2 = "name2"
}
if (this.dataObj.p1 == "name1") {
this.dataObj.p1 = "product1"
} else {
this.dataObj.p1 = "name1"
}
},
changeOthers: function() {
if (this.dataObj.p3 == "name3") {
this.dataObj.p3 = "product3"
} else {
this.dataObj.p3 = "name3"
}
}
},
}
</script>
You can test the change buttons to see that by changing dataObj.p1 or dataObj.p2 or both of them the loadData() method only called once and by changing others it is not called.

for you do ontouch event in vuejs while using it with your HTML inline
and you have an object model that house you other variable and you need to validate the any of the variable you will need to put them in watcher and use qoute ('') to tell vuejs that this is from a the model.email
hope this is useful
data() {
return {
model: {},
error_message: [],
}
},
watch: {
'model.EmailAddress'(value) {
// binding this to the data value in the email input
this.model.EmailAddress = value;
this.validateEmail(value);
},
},
methods: {
validateEmail(value) {
if (/^\w+([\.-]?\w+)*#\w+([\.-]?\w+)*(\.\w{2,3})+$/.test(value)) {
this.error_message['EmailAddress'] = '';
} else {
this.error_message['EmailAddress'] = 'Invalid Email Address';
}
}
},

get index from watched array

I have a vue application where I watch an array for changes. This is working fine. But I'm not sure how to get the index of the array item which has changed, as the watch callback only passes in the old/new values.
Demo: http://jsfiddle.net/q3zd4fmv/
Simplified Example:
new Vue({
el: '#demo',
data: {
things: [{foo:1}, {foo:2}]
},
watch: {
things: {
handler: function (val, oldVal) {
alert('a thing changed')
},
deep: true
}
},
methods: {
change: function () {
this.things[0].foo = 5
}
}
})

Unfortunately, not out of the box. Using a combination of argument destructuring and a custom watch function, you can achieve something that should do it. For example;
new Vue({
el: '#demo',
data: {
things: [{foo:1}, {foo:2}]
},
methods: {
change: function (...args) {
let [thing, after, before] = args;
console.log(thing);
}
},
mounted: function(){
this.things.forEach(thing => {
this.$watch(() => thing, this.change.bind(null, thing))
});
}
})

Bootstrap-vue - Setting table variant dynamically

So I'm using Bootstrap Vue with this test app. I'm trying to change the variant of a table cell depending on the value of it. Unfortunately, the variant parameter will not take a function, so I'm out of ideas on how to achieve this.
This is my code:
var app = new Vue({
el: '#app',
data: {
items: [], //Will be populated through AJAX
fields: [
{
key: 'Vendedor',
label: 'Vendedor'
},
{
key: 'OBJETIVO',
label: 'Objetivo',
formatter: (value) => { return parseFloat(value).toFixed(2)},
variant: estiloObjetivo //THIS IS NOT WORKING
}
]
},
methods: {
Cargar: function () {
var salesperson = getCookie('salespersonCode');
var url_servicio = 'http://MywebService/';
var self = this;
$.ajax({
type: 'GET',
url: url_servicio + 'ventas/' + salesperson,
dataType: "json", // data type of response
success: function(data){
self.items = data
}
});
},
estiloObjetivo (value) {
if value > 0 //I need my cell variant to change depeding on this value
return 'danger'
else
return 'success'
}
}
})
This is my HTML part:
<div id="app">
<button v-on:click="Cargar">Cargar</button>
<b-table striped hover :fields="fields" :items="items"></b-table>
</div>
Any ideas on how to style a Bootstrap-vue cell dynamically?
This is the way it's done in the docs, it's actually set in the "items" array, but how is this useful in cases like mine where I get the data from a web service?:
{
salesperson: 'John',
Objetivo: 2000,
_cellVariants: { salesperson: 'success', Objetivo: 'danger'}
},
So I guess what I need is a way to set the I need is to set the _cellVariants parameter of each element in the 'items' array.

You likely need a computed property. Computed properties automatically update on changes to the reactive variables that they depend on.
The following example implements a computed property, styledItems, which you must use in place of items in the template. It returns a 1-deep copy of items, i.e. a new array containing a copy of each item, with the extra _cellVariants property added.
new Vue({
data: {
items: [ /* your data here */ ]
},
methods: {
estiloObjetivo: value => (value > 0) ? 'danger' : 'success'
},
computed: {
styledItems() {
return this.data.map(datum =>
Object.assign({}, datum, {
_cellVariants: {
Objetivo: this.estiloObjetivo(datum.Objetivo)
}
})
}
})

If you want to add variant to items you could use a computed property called cptItems and define it as follows:
computed:{
cptItems(){
return this.items.map((item)=>{
let tmp=item;
item.OBJETIVO>0?tmp.variant='danger':tmp.variant='success';
return tmp;
})
}
and use that property inside your template like :
<b-table .... :items="cptItems"></b-table>

I was sure the answers above would solve my own issue but they did not. I found a different way to color table cells: https://github.com/bootstrap-vue/bootstrap-vue/issues/1793
This is aside from using variants to color a table cell. Instead, we utilize tdclass and a function.
<script>
new Vue({
el: '#itemView',
data() {
return {
fields: [
{
key: 'Objetive',
sortable: true,
thClass: 'text-nowrap',
tdClass: (value, key, item) => {
return 'table-' + this.getColor(item);
}
}
],
};
},
methods: {
getColor(item) {
return item.Objetive > 0 ? 'danger' : 'success';
},
},
});
</script>
For my own use-case, I needed to compare two cells of the same row, then apply a class to one.
...
{
key: 'DEMAND_QTY',
sortable: true,
thClass: 'text-nowrap',
tdClass: (value, key, item) => {
return 'table-' + this.demandStatusColor(item);
},
},
{ key: 'TOTAL_DEMAND', sortable: true, thClass: 'text-nowrap' },
],
};
},
methods: {
demandStatusColor(item) {
return item.DEMAND_QTY < item.TOTAL_DEMAND ? 'danger' : 'success';
},
}
...
Perhaps this will help someone, if not OP.

#John answer worked for me. I don't have enough reputation to make comment or useful
tdClass: (type, key, item) => {
switch (type) {
case "value":
return "bg-warning text-white";
break;
case "value":
return "bg-danger text-white";
break;
case "value":
return "bg-info text-white";
break;
default:
break;
}
},

Vue props data not updating in child component

Hi everyone I just want some explanation about vue props data. So I'm passing value from parent component to child component. The thing is when parent data has data changes/update it's not updating in child component.
Vue.component('child-component', {
template: '<div class="child">{{val}}</div>',
props: ['testData'],
data: function () {
return {
val: this.testData
}
}
});
But using the props name {{testdata}} it's displaying the data from parent properly
Vue.component('child-component', {
template: '<div class="child">{{testData}}</div>',
props: ['testData'],
data: function () {
return {
val: this.testData
}
}
});
Thanks in advance
Fiddle link

This is best explained with a very simple example
let a = 'foo'
let b = a
a = 'bar'
console.info('a', a)
console.info('b', b)
When you assign...
val: this.testData
you're setting the initial value of val once when the component is created. Changes to the prop will not be reflected in val in the same way that changes to a above are not reflected in b.
See https://v2.vuejs.org/v2/guide/components.html#One-Way-Data-Flow

I resolve with! this.$set(this.mesas, i, event);
data() {
return { mesas: [] }
},
components: {
'table-item': table_l,
},
methods: {
deleteMesa: function(event) {
let i = this.mesas.map(item => item.id).indexOf(event.id);
console.log("mesa a borrare", i);
this.mesas.splice(i, 1);
},
updateMesa: function(event) {
let i =this.mesas.map(item => item.id).indexOf(event.id);
console.log("mesa a actualizar", i);
/// With this method Vue say Warn
//this.mesas[i]=event;
/// i Resolve as follow
this.$set(this.mesas, i, event);
},
// Adds Useres online
addMesa: function(me) {
console.log(me);
this.mesas.push(me);
}
}

How to check when data changes in component by itself with vue js?

I have method that changes data in itself, simple example:
Vue.component('component', {
template: '#component',
data: function () {
return {
dataToBeWatched: ''
}
},
methods: {
change: function (e) {
var that = this;
setTimeOut(function() {
that.dataToBeWatched = 'data changed';
}, 2000);
},
makeSmthWhenDataChanged: function () {
// ajax request when dataToBeWatched changed or when dataToBeWatched isn't empty
}
}
});
How to create such watcher using correct methods vue js?
Or I need to use props watching it in component?

Vue components can have a watch property which is an object. The object keys need to be the name of the prop or data that needs to be watched, and the value is a function that is invoked when the data changes.
https://v2.vuejs.org/v2/guide/computed.html#Computed-vs-Watched-Property
Vue.component('component', {
template: '#component',
data: function () {
return {
dataToBeWatched: ''
}
},
methods: {
change: function (e) {
var that = this;
setTimeOut(function() {
that.dataToBeWatched = 'data changed';
}, 2000);
},
makeSmthWhenDataChanged: function () {
// ajax request when dataToBeWatched changed or when dataToBeWatched isn't empty
}
},
watch: {
dataToBeWatched: function(val) {
//do something when the data changes.
if (val) {
this.makeSmthWhenDataChanged();
}
}
}
});