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Getting following error: Type 'Promise<string[]>' is not assignable to type 'string[]'. Property 'includes' is missing in type 'Promise<string[]>'.
when i cast Promise<string[]> to type 'string[]' My code below,
Component: app.dashboard.ts
import {Component} from '@angular/core'; import { MemberService } from "./app.service"; @Component({ selector:'app-root', templateUrl:'./app.dashboard.html', providers:[MemberService] }) export class AppDashboard{ title='Dashboard' constructor(private memberService: MemberService) { } public doughnutChartLabels:string[] = this.memberService.getmemberheader();//error occurred here } } Service:app.service.ts
import { Injectable } from '@angular/core'; import { Member } from './Member'; import { Http, Response, Headers, RequestOptions, URLSearchParams } from'@angular/http'; import 'rxjs/add/operator/map'; import 'rxjs/add/operator/toPromise'; @Injectable() export class MemberService { constructor(private http: Http) { } private getHeaders(){ // I included these headers because otherwise FireFox // will request text/html instead of application/json let headers = new Headers(); headers.append('Accept', 'application/json'); return headers; } getmemberheader(): Promise<string[]> { return this.http .get(`/ReportService/MemberDatabaseCountryname`, {headers: this.getHeaders()}) .toPromise() .then(this.extractData) .catch(this.handleError); } private extractData(res: Response) { let body = res.json(); return body || {}; } private handleError(error: any): Promise<any> { console.error('An error occurred', error); return Promise.reject(error.message || error); } } 
890
The error "Type is not assignable to type 'never'" occurs when we declare an empty array without explicitly typing it and attempt to mutate the array. To solve the error, explicitly type the empty array, e.g. const arr: string[] = []; .
The error "Argument of type string | undefined is not assignable to parameter of type string" occurs when a possibly undefined value is passed to a function that expects a string . To solve the error, use a type guard to verify the value is a string before passing it to the function.
To access the value of a promise in TypeScript, call the then() method on the promise, e.g. p. then(value => console. log(value)) . The then() method takes a function, which is passed the resolved value as a parameter.
Assume your response from http.get is an array, here you are returning Promise from function memberService.getmemberheader, you should retrieve result of promise at its then callback instead (not assigning promise itself to array doughnutChartLabels).
public doughnutChartLabels: string[]; this.memberService.getmemberheader().then(res => { this.doughnutChartLabels = res; }) If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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