Vue3 Typescript - property does not exist on type issue

Question

I am trying to fill up a component with leads coming from an API. I have a LeadService file as well as my vue template file. The issue I'm having, is I'm using an async call on my template file which works, but when I go to compute the values it throws a property does not exist on type error. It actually works you can see the correct components behind the error message. I can't figure out how to make the error go away.

Here's the service class LeadService.ts

import ApiService from "@/core/services/ApiService";

interface Lead {
  id: string;
  first_name: string;
  last_name: string;
  lead_form_name: string;
  email: string;
  campaign: string;
  timestamp: number;
  mobile_number: string;
  message: string;
  medium: string;
  city: string;
  state: string;
  leadType: string;
  quality: string;
  source: string;
  call_link: string;
  company: string;
  country: string;
}

export default class LeadService {

  getLeads() {

    const accountInfo = JSON.parse(localStorage.getItem('accountInfo') || '{}');

    ApiService.setHeader();

    return ApiService.query("/leads", {params: {client_id : accountInfo.client_id}})
      .then(({ data }) => {
        let leadData: Lead[] = data['Items'];
        return leadData;
      })
      .catch(({ response }) => {
        return response;
      });

  }
}

Here is my vue template Leads.vue

<template>
  <!--begin::Leads-->
  <div class="row gy-5 g-xl-8 mb-8">
    <div class="col-xxl-12">
      <LeadTracker
        :lead-data="leadData"
        :updateQuality="updateQuality"
        :key="componentKey"
      />
    </div>
  </div>

  <div class="row gy-5 gx-xl-8 mb-8">
    <div class="col-xxl-8">
      <LeadMethods
        chart-height="500"
        :method-data="getLeadMethods"
      ></LeadMethods>
    </div>
  </div>
  <!--end::Leads-->
</template>

<script lang="ts">
import { defineComponent, onMounted } from "vue";
import { setCurrentPageTitle } from "@/core/helpers/breadcrumb";
import LeadMethods from "@/components/leads/methods/LeadMethods.vue";
import LeadTracker from "@/components/leads/tracker/LeadTracker.vue";
import LeadService from "@/core/services/LeadService";
import ApiService from "@/core/services/ApiService";

export default defineComponent({
  name: "leads",
  components: {
    LeadMethods,
    LeadTracker,
  },
  data() {
    return {
      leadData: {},
    }
  },
  beforeMount: async function() {
    this.leadData = await new LeadService().getLeads()
  },
  setup() {
    onMounted(() => {
      setCurrentPageTitle("Lead Activity");
    });

    const sourceThreshold = 5;

    return {
      sourceThreshold,
      componentKey: 0
    };
  },
  computed: {
    getLeadMethods(): object {
      const leadMethods: Array<object> = [];
      const totalLeads = this.leadData.length;

      console.log('called getLeadMethods check this.leadData', this.leadData);

      // Get the total number of Paid Media leads
      const totalPaid = this.leadData.filter(
        lead => lead.medium == "paid_media"
      ).length;

      // Get the total number of Calls
      const totalCall = this.leadData.filter(lead => lead.leadType == "call")
        .length;

      // Separate form leads from the rest
      const formData = this.leadData.filter(lead => lead.leadType == "form");

      // Make array for form names
      const formTypes: Array<string> = [];
      this.leadData.filter(lead => {
        if (!formTypes.includes(lead.lead_form_name))
          formTypes.push(lead.lead_form_name);
      });

      // Create objects for each form by name, push to leadMethods
      formTypes.filter(type => {
        let totalFormLeads = 1;
        formData.filter(form => {
          if (form.lead_form_name == type) totalFormLeads++;
        });
        const formMethod = {
          name: type,
          description: "Lorem ipsum dolor sit amet, consectetur.",
          total: totalFormLeads,
          percent: Math.round((totalFormLeads / totalLeads) * 100)
        };
        leadMethods.push(formMethod);
      });

      const callTracking = {
        name: "Location Based Call-Tracking",
        description: "Lorem ipsum dolor sit amet, consectetur.",
        total: totalCall,
        percent: Math.round((totalCall / totalLeads) * 100)
      };
      const paidSearch = {
        name: "Paid Search",
        description: "Lorem ipsum dolor sit amet, consectetur.",
        total: totalPaid,
        percent: Math.round((totalPaid / totalLeads) * 100)
      };

      leadMethods.push(callTracking, paidSearch);

      return leadMethods;
    }
  }
});
</script>

The problem begins in my computed functions, where I start filtering this.LeadData Essentially every filter throws a Property does not exist on type error, but they do exist.

It's important to note, that when this.leadData gets set, it is a Proxy. Any help would be appreciated, I was wondering if I could just suppress the error although I don't like that solution.

For instance, in my first filter in the computed methods

// Get the total number of Paid Media leads
      const totalPaid = this.leadData.filter(
        lead => lead.medium == "paid_media"
      ).length;

medium is a property of leadData and I can actually console log it and it works just fine, but it still always throws the property does not exist on type .

Answer 1

The type of leadData is inferred from its declaration in data() . It's initialized to {} , which means its type is an immutable empty object (and no properties can be attached to it). However, leadData is eventually assigned the return of LeadService().getLeads() , so its type should actually be an array of Lead objects.

To properly type leadData , initialize it to an empty array with a type assertion of Lead[] :

export default defineComponent({
  data() {
    return {
      //leadData: {}, ❌
      leadData: [] as Lead[], ✅
    }
  }
})