Async call for computed property - Vue.js - ajax

Question

I have a computed property that will only be used if a match for a property exists. Because of this, I'm making the call to get the data asynchronous so that it's only retrieved when needed. I'm having an issue though trying to make an async call to return data for a computed property.
Below is what I have:
new Vue({
el: "#formCompleteContainer",
data: {
form: {},
components: []
},
computed: {
employeeList: function () {
var self = this;
if (_.some(this.components, function (component) {
return component.ComponentInfo.Type === 8
})) {
var employees = [];
$.ajax({
url: "/Form/GetAllUsers",
type: "GET"
}).done(function (results) {
employees = results;
});
return employees;
} else {
return [];
}
}
}
});
I know this isn't working because I'm returning before the call is complete. I've seen how to use deferredobjects and what not but I can't seem to figure out how to implement it with Vue.

Answer 1

For your use case, I don't think computed property can implement the goal.
My solution:
create one data property as one 'defered' object,
then uses one watch to async call your backend to get new data, finally assign to the defered object
like below demo:
Vue.config.productionTip = false
app = new Vue({
el: "#app",
data: {
product: "Boots",
deferedProduct: ''
},
watch: {
product: function (newVal, oldVal) {
setTimeout(() => {
this.deferedProduct = 'Cats in ' + newVal + '!'
}, 1500)
}
},
methods: {
nextProduct: function () {
this.product += 'a'
}
}
})
<script src="https://unpkg.com/vue#2.5.16/dist/vue.js"></script>
<div id="app">
<button #click="nextProduct()">Click Me!</button>
<h2>{{product}}</h2>
<h2>{{deferedProduct}}</h2>
</div>

Answer 2

This is what vue-async-computed is meant for. It resolves the promise you returned and handles any race conditions.
new Vue({
el: "#formCompleteContainer",
data: {
form: {},
components: []
},
asyncComputed: {
employeeList: function () {
if (_.some(this.components, function (component) {
return component.ComponentInfo.Type === 8
})) {
return $.ajax({
url: "/Form/GetAllUsers",
type: "GET"
});
} else {
return Promise.resolve([]);
}
}
}
});

Answer 3

After doing some more research I have gone another route. I agree with Sphinx that I don't think what I am trying to achieve will work with a computed property.
Instead, this is what I am going with:
new Vue({
el: "#formCompleteContainer",
data: {
form: {},
components: [],
employees: []
},
methods: {
getEmployees: function () {
var self = this;
if (_.some(this.components, function (component) {
return component.ComponentInfo.Type === 8;
})) {
$.ajax({
url: "/Form/Form/GetAllUsers",
type: "GET"
}).done(function (results) {
self.employees = results;
});
}
}
},
created: function () {
this.form = pageModel.Form;
this.components = pageModel.Components;
},
mounted: function () {
this.getEmployees();
}
});

Answer 4

As pointed out already, mounted and other 3rd party solutions can work.
However, better readability and component loading will come from putting the desired Promise within a data property. And then using the Vue lifecycle hook created, we can wait for that Promise to resolve with a .then.
For example:
requestService.js:
...
async foo(){
let myRequest = someRequest.createInstance()
await myRequest.onReady()
return myRequest.getSomePromise()
}
...
And then import the service into your component, as well as declaring a data prop:
myComponent.vue
...
data: (){
myPromiseLoc: null,
}
...
created: (){
requestService.foo().then( result =>
{
this.myPromiseLoc = result
}
}
...