Vue - Deep watching an array of objects and calculating the change?
I have an array called people that contains objects as follows:
Before
[
{id: 0, name: 'Bob', age: 27},
{id: 1, name: 'Frank', age: 32},
{id: 2, name: 'Joe', age: 38}
]
It can change:
After
[
{id: 0, name: 'Bob', age: 27},
{id: 1, name: 'Frank', age: 33},
{id: 2, name: 'Joe', age: 38}
]
Notice Frank just turned 33.
I have an app where I am trying to watch the people array and when any of the values changes then log the change:
<style>
input {
display: block;
}
</style>
<div id="app">
<input type="text" v-for="(person, index) in people" v-model="people[index].age" />
</div>
<script>
new Vue({
el: '#app',
data: {
people: [
{id: 0, name: 'Bob', age: 27},
{id: 1, name: 'Frank', age: 32},
{id: 2, name: 'Joe', age: 38}
]
},
watch: {
people: {
handler: function (val, oldVal) {
// Return the object that changed
var changed = val.filter( function( p, idx ) {
return Object.keys(p).some( function( prop ) {
return p[prop] !== oldVal[idx][prop];
})
})
// Log it
console.log(changed)
},
deep: true
}
}
})
</script>
I based this on the question that I asked yesterday about array comparisons and selected the quickest working answer.
So, at this point I expect to see a result of: { id: 1, name: 'Frank', age: 33 }
But all I get back in the console is (bearing in mind i had it in a component):
[Vue warn]: Error in watcher "people"
(found in anonymous component - use the "name" option for better debugging messages.)
And in the codepen that I made, the result is an empty array and not the changed object that changed which would be what I expected.
If anyone could suggest why this is happening or where I have gone wrong here then it would be greatly appreciated, many thanks!
Answer
Your comparison function between old value and new value is having some issue. It is better not to complicate things so much, as it will increase your debugging effort later. You should keep it simple.
The best way is to create a person-component and watch every person separately inside its own component, as shown below:
<person-component :person="person" v-for="person in people"></person-component>
Please find below a working example for watching inside person component. If you want to handle it on parent side, you may use $emit to send an event upwards, containing the id of modified person.
Vue.component('person-component', {
props: ["person"],
template: `
<div class="person">
{{person.name}}
<input type='text' v-model='person.age'/>
</div>`,
watch: {
person: {
handler: function(newValue) {
console.log("Person with ID:" + newValue.id + " modified")
console.log("New age: " + newValue.age)
},
deep: true
}
}
});
new Vue({
el: '#app',
data: {
people: [
{id: 0, name: 'Bob', age: 27},
{id: 1, name: 'Frank', age: 32},
{id: 2, name: 'Joe', age: 38}
]
}
});<script src="https://unpkg.com/[email protected]/dist/vue.js"></script>
<body>
<div id="app">
<p>List of people:</p>
<person-component :person="person" v-for="person in people"></person-component>
</div>
</body>