Use the following:

Validators.pattern(/^\S*$/)

DEMO

space Not allowed

let nospacePattern = [a-zA-Z0-9]

Update

As per requirement in comment section.

need pattern not to allow only spaces. (space in between words are allowed).but when user enter spaces in input and try to save it then it should not allow to save

Validators.pattern(".*\\S.*[a-zA-z0-9 ]");

Update 2

Better and Cleaner way to use custom validation pattern like below -

controlName: ['', [Validators.required, this.noWhitespaceValidator]],

....
....
noWhitespaceValidator(control: FormControl) {
    const isWhitespace = (control && control.value && control.value.toString() || '').trim().length === 0;
    const isValid = !isWhitespace;
    return isValid ? null : { 'whitespace': true };
  }

try this, it will return false while sapce key press :

@Component({
  selector: 'my-app',
  template: `
    <div>
       <input class="form-control" type="number" formControlName="pinCode" placeholder="Pin Code"
             (keydown.space)="$event.preventDefault()">
    </div>
  `,
  providers: [myService]
})

visit for more Events :

https://developer.mozilla.org/en-US/docs/Web/Events