很简单：

const isPlaceholderOverflowed = inputId => {
  const input = document.getElementById(inputId);
  input.value = input.placeholder;
  const isOverflowed = input.scrollWidth > input.clientWidth;
  input.value = "";
  return isOverflowed;
}

感谢@MasihJahangiri的回答，我设法在Angular -14：

@Directive({
    selector: '[AutoResizeInput]',
})
export class AutoResizeInputDirective implements OnInit {
    @Input() clientPlaceholder = '';

    constructor(private elementRef: ElementRef) {}

    ngOnInit(): void {
        const input = this.elementRef.nativeElement;

        if (!this.clientPlaceholder.length || this.clientPlaceholder == undefined || this.clientPlaceholder == null) {
            throw new Error('AutoResizeInputDirective - Input element must have "clientPlaceholder" property defined!');
        }

        input.setAttribute('value', this.clientPlaceholder);
        const css = `width: ${input.scrollWidth}px`;
        this.elementRef.nativeElement.setAttribute('style', css);
        input.value = '';
    }
}

在模板中添加了Input元素：

<input
    cbpAutoResizeInput
    [clientPlaceholder]="item.placeholder"
    ... />