Angular Constant & Global Variables | Angular 9, 8, 7, 6, 5, 4, 2

How to CREATE constant in your Angular Apps? 

A constant is a value that can’t be changed by the program during normal execution.

                                                                 OR

Constants are of fixed values that do not change during the execution of a program. There are various types of constants. These can be :-

1.      Numeric

2.      Character

3.      Integer

4.      Other types

And constant class looks like –

export class AppConstants {

    public static get baseURL(): string { return "http://localhost:4200/api"; }

}

And Use of constant in Services –

import { Injectable } from '@angular/core';

import {HttpClient, HttpParams, HttpHeaders} from "@angular/common/http";

import { Employee } from './employee';

import{ AppConstants} from '../app/constants'

@Injectable()

export class EmployeeService {

 

  //variable initialization

  headers : any;

  _baseURL : string;

  //constructor initialization

  constructor(private _htc:HttpClient) {

      this.headers = new HttpHeaders().set('content-type', 'application/json');

      this._baseURL = AppConstants.baseURL;

  }

  // POST employee - for creating a New employee.

  addEmployee(emp :any){

    var employee = {

        name:emp.name,

        Dep:emp.Dep,

        Des:emp.Des 

    } 

    return this._htc.post<Employee>(this._baseURL+'/Employees/Add', employee, (this.headers));

  }

  //DELETE employee - for delete employee.

  deleteEmployee(id :string){    

    return this._htc.delete<Employee>(this._baseURL+'/Employees/Delete/'+id);

  }

}