Unable to get data in apex chart - vue.js

Question

I am trying to use spline area chart of apex chart in my vue js application , and extracting date in the format of timestamp from Firestore in created part of the application and is to be shown in the x axis but x axis in not displaying the timestamp and giving error .
here is the code
export default {
data() {
return {
options : { year: "numeric", month: "numeric",
day: "numeric" },
timestamp:[],
RecruiterChart: {
series: [{
name: 'Total Jobs Posted',
data: [11, 32, 45, 32, 34, 52, 41]
}, {
name: 'Applied Candidates',
data: [31, 40, 28, 51, 42, 109, 100]
}],
chartOptions: {
dataLabels: {
enabled: false
},
stroke: {
curve: 'smooth'
},
colors: themeColors,
xaxis: {
type: 'datetime',
categories: []
},
tooltip: {
x: {
format: 'dd/MM/yyyy'
},
}
}
},
}
},
components: {
VueApexCharts
},
created(){
const thisIns = this;
var u= firebase.auth().currentUser
let Ref=firebase.firestore().collection("Recruiter").doc(u.uid).collection("Jobs")
Ref.orderBy("timestamp", "desc").onSnapshot(function(snapshot){
$.each(snapshot.docChanges(), function(){
var change= this
if(change.type==="added"){
var ab = change.doc.data().timestamp.toDate().toLocaleString("en-CH", thisIns.options)
thisIns.time.push(ab)
thisIns.RecruiterChart.chartOptions.xaxis.categories.push(
ab
)
console.log( thisIns.RecruiterChart.chartOptions.xaxis.categories)
}
})
})
console.log(thisIns.RecruiterChart.chartOptions.xaxis.categories)
},
}
but the graph is giving error
Error: attribute cx: Expected length, "NaN".