title: How to prevent canvas drawing to be erased on next mousedown?
body: <p>I am on Ionic 3 angular V5, I couldn't use the Viewchild which returns a undefined, so I used ViewChildren et get the first item of the array (dirty I know)</p>
  <pre><code>@ViewChildren('imageCanvas') canvas: any;
  public canvasElement: any;
  saveX: number;
  saveY: number;
  public drawing = false;
  selectedColor: '#9e2956';
  lineWidth: 5;
  
  startDrawing(ev) {
      if (this.canvasElement === undefined) {
          this.canvasElement = this.canvas._results[0].nativeElement;
          console.log('always there')
      }
      this.canvasElement.width = this.plt.width() + '';
      this.canvasElement.height = 200;
  
      const canvasPosition = this.canvasElement.getBoundingClientRect();
      let currentX = ev.pageX - canvasPosition.x;
      let currentY = ev.pageY - canvasPosition.y;
      this.saveX = currentX;
      this.saveY = currentY;
  
      this.drawing = true
  }
  
  moved(ev) {
      if (!this.drawing) return
  
  
      const canvasPosition = this.canvasElement.getBoundingClientRect();
  
      //console.log('canvasPosition ', canvasPosition)
  
      let ctx = this.canvasElement.getContext('2d');
  
      let currentX = ev.pageX - canvasPosition.x;
      let currentY = ev.pageY - canvasPosition.y;
  
      ctx.lineJoin = 'round';
      ctx.strokeStyle = this.selectedColor;
      ctx.lineWidth = this.lineWidth;
  
      ctx.beginPath();
      ctx.moveTo(this.saveX, this.saveY);
      ctx.lineTo(currentX, currentY);
      ctx.closePath();
  
      ctx.stroke();
  
      this.saveX = currentX;
      this.saveY = currentY;
  
  
  }
  </code></pre>
  <p>When I inish a line, I release the button, and drawing again will erase the previous drawing</p>