How to access local component variable from a callback in vue? - vue.js

Question

I am trying to set my components variable using an api rest command. I wanted to handle all responses through a function in its own file called handleResponse() which is below.
// api/tools/index.js
function handleResponse (promise, cb, cbError) {
var cbErrorRun = (cbError && typeof cb === "function")
promise.then(function (response) {
if (!response.error) {
cb(response)
}
else if (cbErrorRun) {
cbError(response)
}
}).catch(function (error) {
console.log(error)
if (cbErrorRun) {
var responseError = {
"status": 404,
"error": true,
"message": error.toString()
}
cbError(responseError)
}
})
}
export {handleResponse}
In my component file I have this
.... More above....
<script>
import { fetchStock } from '#/api/stock'
export default {
data () {
return {
stock: {},
tabs: [
{
title: 'Info',
id: 'info'
},
{
title: 'Listings',
id: 'listings'
},
{
title: 'Company',
id: 'company'
}
],
}
},
validate ({params}) {
return /^\d+$/.test(params.id)
},
created: function() {
var params = {'id': this.$route.params.stockId}
//this.$route.params.stockId}
fetchStock(
params,
function(response) { //on successful data retrieval
this.stock = response.data.payload // payload = {'name': test123}
console.log(response)
},
function(responseError) { //on error
console.log(responseError)
}
)
}
}
</script>
The current code gives me this error: "Uncaught (in promise) TypeError: Cannot set property 'stock' of undefinedAc". I think this happens because I no longer have access to 'this' within the callback I pass in the fetchStock function. How would I fix this without changing the current handleResponse layout.

Answer 1

You can try this trick
created: function() {
var params = {'id': this.$route.params.stockId}
//this.$route.params.stockId}
var self = this;
fetchStock(
params,
function(response) { //on successful data retrieval
self.stock = response.data.payload // payload = {'name': test123}
console.log(response)
},
function(responseError) { //on error
console.log(responseError)
}
)
}

Answer 2

You can either use an arrow function for you callback since arrow functions maintain and use the this of their containing scope:
created: function() {
var params = {'id': this.$route.params.stockId}
//this.$route.params.stockId}
fetchStock(
params,
(response) => { //on successful data retrieval
self.stock = response.data.payload // payload = {'name': test123}
console.log(response)
},
(responseError) => { //on error
console.log(responseError)
}
)
}
Or you can assign const vm = this n the beginning of your method before the callbacks like so.
vm stands for "View Model"
created: function() {
var params = {'id': this.$route.params.stockId}
//this.$route.params.stockId}
const vm = this;
fetchStock(
params,
function(response) { //on successful data retrieval
self.stock = response.data.payload // payload = {'name': test123}
console.log(response)
},
function(responseError) { //on error
console.log(responseError)
}
)
}
I advise using the const as opposed to var in the vm declaration to make it obvious the value of vm is a constant.