Simple web calculator: Added special button event handling

handle-button-click.ts.diff

#handleButtonClick(event: Event): void {
  const target = event.target as HTMLButtonElement;
  if (target === null) {
    return;
  }

  const { value } = target;
  const userValue = target.innerText;

+ switch (value) {
+  case 'ac':
+     this.query = '';
+     break;
+   case 'ce':
+     this.query = this.query.slice(0, -1);
+     break;
+   case '=':
+     this.#performCalculation();
+     break;
+   default:
+     this.query += userValue;
+ }
}