Solution 1: Copy any text

HTML

<button (click)="copyMessage('This goes to Clipboard')" value="click to copy" >Copy this</button>

.ts file

copyMessage(val: string){
    const selBox = document.createElement('textarea');
    selBox.style.position = 'fixed';
    selBox.style.left = '0';
    selBox.style.top = '0';
    selBox.style.opacity = '0';
    selBox.value = val;
    document.body.appendChild(selBox);
    selBox.focus();
    selBox.select();
    document.execCommand('copy');
    document.body.removeChild(selBox);
  }

Solution 2: Copy from a TextBox

HTML

 <input type="text" value="User input Text to copy" #userinput>
      <button (click)="copyInputMessage(userinput)" value="click to copy" >Copy from Textbox</button>

.ts file

    /* To copy Text from Textbox */
  copyInputMessage(inputElement){
    inputElement.select();
    document.execCommand('copy');
    inputElement.setSelectionRange(0, 0);
  }

Demo Here

Solution 3: Import a 3rd party directive ngx-clipboard

<button class="btn btn-default" type="button" ngxClipboard [cbContent]="Text to be copied">copy</button>

Solution 4: Custom Directive

If you prefer using a custom directive, Check Dan Dohotaru's answer which is an elegant solution implemented using ClipboardEvent.

Solution 5: Angular Material

Angular material 9 + users can utilize the built-in clipboard feature to copy text. There are a few more customization available such as limiting the number of attempts to copy data.

I know this has already been highly voted in here by now, but I'd rather go for a custom directive approach and rely on the ClipboardEvent as @jockeisorby suggested, while also making sure the listener is correctly removed (same function needs to be provided for both the add and remove event listeners)

stackblitz demo

import { Directive, Input, Output, EventEmitter, HostListener } from "@angular/core";

@Directive({ selector: '[copy-clipboard]' })
export class CopyClipboardDirective {

  @Input("copy-clipboard")
  public payload: string;

  @Output("copied")
  public copied: EventEmitter<string> = new EventEmitter<string>();

  @HostListener("click", ["$event"])
  public onClick(event: MouseEvent): void {

    event.preventDefault();
    if (!this.payload)
      return;

    let listener = (e: ClipboardEvent) => {
      let clipboard = e.clipboardData || window["clipboardData"];
      clipboard.setData("text", this.payload.toString());
      e.preventDefault();

      this.copied.emit(this.payload);
    };

    document.addEventListener("copy", listener, false)
    document.execCommand("copy");
    document.removeEventListener("copy", listener, false);
  }
}

and then use it as such

<a role="button" [copy-clipboard]="'some stuff'" (copied)="notify($event)">
  <i class="fa fa-clipboard"></i>
  Copy
</a>

public notify(payload: string) {
   // Might want to notify the user that something has been pushed to the clipboard
   console.info(`'${payload}' has been copied to clipboard`);
}

Note: notice the window["clipboardData"] is needed for IE as it does not understand e.clipboardData

I think this is a much more cleaner solution when copying text:

copyToClipboard(item) {
    document.addEventListener('copy', (e: ClipboardEvent) => {
      e.clipboardData.setData('text/plain', (item));
      e.preventDefault();
      document.removeEventListener('copy', null);
    });
    document.execCommand('copy');
  }

And then just call copyToClipboard on click event in html. (click)="copyToClipboard('texttocopy')".