Cannot read property 'push' of undefined(…) in angular2

Question

this is the error saying " cannot read property 'push' of undefined " when using the code below

  let deal = new Deal(  5, 'afaf', 'dafa',5,23 )    this.publicDeals.push( deal )   // gives a error saying Cannot read property 'push' of undefined(…) 

The whole is shown below

export class Deal {    constructor(     public id: number,     public name: string,     public  description: string,     public originalPrice: number,     public salePrice: number       ) { }     } 

In another component,

import { Component, OnInit } from '@angular/core';  import { Deal } from '../deal'; import { DealService } from '../deal.service';  @Component({   selector: 'public-deals',   templateUrl: 'public-deals.component.html',   styleUrls: ['public-deals.component.css'] })  export class PublicDealsComponent implements OnInit {   publicDeals: Deal[];    constructor(     private dealService: DealService) {   }    ngOnInit(): void {           let deal = new Deal(  5, 'afaf', 'dafa',5,23 )        this.publicDeals.push( deal )   // gives a error saying Cannot read property 'push' of undefined(…)    }    purchase(item){     alert("You bought the: " + item.name);   } } 

Answer 1

publicDeals is not initiated;

publicDeals: Deal[] = [];