In relation to the characteristics of an Angular Component (written in TypeScript) Class

I am attempting to create a circle on a canvas using Angular. I have followed the necessary steps and have a basic understanding of how everything works. Although my IDE is not showing any errors, when I run the code, the console displays an error stating "this.circleApp is undefined". I have made multiple attempts to access properties of the circleApp Object where I plan to store most of my application's data and logic, such as calculating radians from degrees to determine the coordinates of my shapes. As a beginner in Angular and TypeScript, I feel like I am overlooking something obvious. Any guidance or links to relevant documentation would be greatly appreciated. Here is an illustration of where I believe the issue lies

Currently, I am only assigning a random number to the "degrees" property, but I plan to connect it to an input later on.

import { ViewChild, Component, OnInit, ElementRef } from "@angular/core";
import { CircleApp } from "./circleApp";
@Component({
  selector: "app-make-circle",
  templateUrl: "./make-circle.component.html",
  styleUrls: ["./make-circle.component.css"]
})
export class MakeCircleComponent implements OnInit {
  circleApp: CircleApp = {
    degrees: 3,
    degreesToRadiansFlipped: function(degree) {
      return (-degree * Math.PI) / 180;
    },
    radian: this.circleApp.degreesToRadiansFlipped(this.circleApp.degrees),
    x: Math.cos(this.circleApp.radian * 200 + 500),
    y: Math.sin(this.circleApp.radian * 200 + 500)
  };
  @ViewChild("myCanvas") myCanvas: ElementRef;
  public context: CanvasRenderingContext2D;
  constructor() {}
  ngOnInit() {}
  ngAfterViewInit(): void {
    this.context = (this.myCanvas
      .nativeElement as HTMLCanvasElement).getContext("2d");
    this.draw();
  }
  private draw() {
    this.context.beginPath();
    this.context.arc(500, 300, 200, 0, Math.PI * 2);
    this.context.moveTo(500, 300);
    this.context.lineTo(this.circleApp.x, this.circleApp.y);
    this.context.stroke();
  }
}

Answer №1

It appears that the problem lies within these specific lines (well, maybe they are just one of the problems):

    radian: this.circleApp.degreesToRadiansFlipped(this.circleApp.degrees),
    x: Math.cos(this.circleApp.radian * 200 + 500),
    y: Math.sin(this.circleApp.radian * 200 + 500)

By referencing this.circleApp within this.circleApp, which does not exist yet, you are essentially attempting to do the following:

let foo = { a: "A", b: foo.a + "B" };

If you substitute the references to this.circleApp on the right-hand side with numerical values or comment them out, the error should disappear.

All you need to do is initialize circleApp in a different manner. If it is a class, simply include

this.circleApp = new CircleApp(/* parameters here */)
early enough in the component's life cycle, such as in ngOnInit.

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