message: refactor(compiler): Remove unnecessary assignment
  This is well known problem and has a opened issue at microsoft/typescript. will highlight an error when this is fixed.
  PR Close
diff: @@ -353,10 +353,9 @@ class _Scanner {
  while (this.peek != quote) {
  if (this.peek == chars.$BACKSLASH) {
  buffer += input.substring(marker, this.index);
  - this.advance();
  let unescapedCode: number;
  - // Workaround for TS2.1-introduced type strictness
  - this.peek = this.peek;
  + this.advance(); // mutates this.peek
  + // @ts-expect-error see microsoft/TypeScript#9998
  if (this.peek == chars.$u) {
  // 4 character hex code for unicode character.
  const hex: string = input.substring(this.index + 1, this.index + 5);
  