(lint/types): fix or ignore remaining lint type errors

- use TS 3.0 defaultProps support so that clearOnResize doesn't have to
  be optional

- ignore consistent-type-assertions and no-non-null-assertion in places
  where those hacks were intentionally used for simplicity's sake

- fix some strict-boolean-expressions by checking for types explicitly
  or using nullish coalescing
  - nullish coalescing on canvasProps isn't breaking because it already
    had PropTypes.object defined
  - nullish coalescing on DPR isn't breaking because it should be a
    number (or undefined), and shouldn't be 0
    - and even if it were 0, it would've been set to 1 before anyway
      bc of the Math.max

- ignore several strict-boolean-expressions in _resizeCanvas because
  checking for undefined specifically is a breaking change
  - 0, '', null, etc falsey width/height was still resized previously,
    so if we check for undefined instead, it will stop resizing falseys
    - 0, '', null, etc don't make a lot of sense to set a width/height,
      if these were used it may have been accidental or for some
      temporary hack
      - accidental would be a bug, so will consider a fix, but fixing
        that bug would still be breaking :/ :/

src/index.tsx

@@ -5,7 +5,7 @@ import trimCanvas from 'trim-canvas'
 
 export interface SignatureCanvasProps extends SignaturePad.SignaturePadOptions {
  canvasProps?: React.CanvasHTMLAttributes<HTMLCanvasElement>
- clearOnResize?: boolean
+ clearOnResize: boolean
 }
 
 export class SignatureCanvas extends Component<SignatureCanvasProps> {
@@ -25,16 +25,18 @@ export class SignatureCanvas extends Component<SignatureCanvasProps> {
  clearOnResize: PropTypes.bool
  }
 
- static defaultProps = {
+ static defaultProps: Pick<SignatureCanvasProps, 'clearOnResize'> = {
  clearOnResize: true
  }
 
  // this is some hack-ish init and casting to avoid `| null` everywhere :/
+ /* eslint-disable @typescript-eslint/consistent-type-assertions */
  _sigPad: SignaturePad = {} as SignaturePad
  _canvas: HTMLCanvasElement = {} as HTMLCanvasElement
+ /* eslint-enable @typescript-eslint/consistent-type-assertions */
 
  private readonly setRef = (ref: HTMLCanvasElement | null): void => {
- if (ref) {
+ if (ref !== null) {
  this._canvas = ref
  }
  }
@@ -70,6 +72,7 @@ export class SignatureCanvas extends Component<SignatureCanvasProps> {
  const copy = document.createElement('canvas')
  copy.width = this._canvas.width
  copy.height = this._canvas.height
+ // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
  copy.getContext('2d')!.drawImage(this._canvas, 0, 0)
  // then trim it
  return trimCanvas(copy)
@@ -87,10 +90,13 @@ export class SignatureCanvas extends Component<SignatureCanvasProps> {
  this._resizeCanvas()
  }
 
+ // a few eslint disables of strict-boolean-expressions here because changing
+ // these lines would be breaking -- 0s, '', null etc are falsey
  _resizeCanvas = (): void => {
- const canvasProps = this.props.canvasProps || {}
+ const canvasProps = this.props.canvasProps ?? {}
  const { width, height } = canvasProps
  // don't resize if the canvas has fixed width and height
+ // eslint-disable-next-line @typescript-eslint/strict-boolean-expressions
  if (width && height) {
  return
  }
@@ -99,14 +105,17 @@ export class SignatureCanvas extends Component<SignatureCanvasProps> {
  /* When zoomed out to less than 100%, for some very strange reason,
  some browsers report devicePixelRatio as less than 1
  and only part of the canvas is cleared then. */
- const ratio = Math.max(window.devicePixelRatio || 1, 1)
+ const ratio = Math.max(window.devicePixelRatio ?? 1, 1)
 
+ // eslint-disable-next-line @typescript-eslint/strict-boolean-expressions
  if (!width) {
  canvas.width = canvas.offsetWidth * ratio
  }
+ // eslint-disable-next-line @typescript-eslint/strict-boolean-expressions
  if (!height) {
  canvas.height = canvas.offsetHeight * ratio
  }
+ // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
  canvas.getContext('2d')!.scale(ratio, ratio)
  this.clear()
  }