ng-autosize/src/autosize.directive.ts

Angular Directive that automatically adjusts textarea height to fit content

import { Input, AfterViewInit, ElementRef, HostListener, Directive} from '@angular/core';

@Directive({
    selector: 'textarea[autosize]'
})

export class Autosize implements AfterViewInit {

    private el: HTMLElement;
    private _minHeight: string;
    private _maxHeight: string;
    private _lastHeight: number;
    private _clientWidth: number;

    @Input('minHeight')
    get minHeight() { 
      return this._minHeight;
    }
    set minHeight(val: string) {
      this._minHeight = val;
      this.updateMinHeight();
    }

    @Input('maxHeight')
    get maxHeight() {
      return this._maxHeight; 
    }
    set maxHeight(val: string) {
      this._maxHeight = val;
      this.updateMaxHeight();
    }

 @HostListener('window:resize', ['$event.target'])
    onResize(textArea: HTMLTextAreaElement) {
      //Only apply adjustment if element width had changed.
      if (this.el.clientWidth === this._clientWidth) return;
      this._clientWidth = this.element.nativeElement.clientWidth;
      this.adjust();
    }

 @HostListener('input',['$event.target'])
  onInput(textArea: HTMLTextAreaElement): void {
    this.adjust();  
  }

  constructor(public element: ElementRef){
    this.el = element.nativeElement;
    this._clientWidth = this.el.clientWidth;
  }

  ngAfterViewInit(): void{
    // set element resize allowed manually by user
    const style = window.getComputedStyle(this.el, null);
    if (style.resize === 'both') {
			this.el.style.resize = 'horizontal';
		}
    else if (style.resize === 'vertical') {
			this.el.style.resize = 'none';
    }
    // run first adjust
    this.adjust();
  }

  adjust(): void{
    // perform height adjustments after input changes, if height is different
    if (this.el.style.height == this.element.nativeElement.scrollHeight + "px") return;
    this.el.style.overflow = 'hidden';
    this.el.style.height = 'auto';
    this.el.style.height = this.el.scrollHeight + "px";
  }

  updateMinHeight(): void{
    // Set textarea min height if input defined
    this.el.style.minHeight = this._minHeight + 'px';
  }

  updateMaxHeight(): void{
    // Set textarea max height if input defined
    this.el.style.maxHeight = this._maxHeight + 'px';
  }

}