This used prevent the typing in input based on key code. In this directive we can give two type number, alphanumeric and alphabets.

keyBoardPrevent.directive.ts

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

@Directive({
    // tslint:disable-next-line:directive-selector
    selector: '[keyPrevent]'
})
export class KeyPreventDirective {

    constructor(private el: ElementRef) { }

    @Input() OnlyNumber: boolean;
    @Input() Alphabets: boolean;
    @Input() Alphanumeric: boolean;
    @Input() OnlyNumberWihtoutDecimel: boolean;

    @HostListener('keydown', ['$event']) onKeyDown(event) {
        const e = <KeyboardEvent>event;
        if ([46, 8, 9, 27, 13, 110, 190].indexOf(e.keyCode) !== -1 ||
            // Allow: Ctrl+A
            (e.keyCode === 65 && (e.ctrlKey || e.metaKey)) ||
            // Allow: Ctrl+C
            (e.keyCode === 67 && (e.ctrlKey || e.metaKey)) ||
            // Allow: Ctrl+V
            // (e.keyCode === 86 && (e.ctrlKey || e.metaKey)) ||
            // Allow: Ctrl+X
            (e.keyCode === 88 && (e.ctrlKey || e.metaKey)) ||
            // Allow: home, end, left, right
            (e.keyCode >= 35 && e.keyCode <= 39)) {
            // let it happen, don't do anything
            return;
        }
        if (this.OnlyNumber) {
            // Ensure that it is a number and stop the keypress
            if ((e.shiftKey || (e.keyCode < 48 || e.keyCode > 57)) && (e.keyCode < 96 || e.keyCode > 105)) {
                e.preventDefault();
            }
        } else if (this.Alphabets) {
            // Ensure that it is a alphabets and stop the keypress
            if (e.keyCode < 65 || e.keyCode > 90) {
                e.preventDefault();
            }
        } else if (this.Alphanumeric) {
            // Ensure that it is a number and stop the keypress
            if ((e.shiftKey || (e.keyCode < 48 || e.keyCode > 57)) && (e.keyCode < 96 || e.keyCode > 105) &&
                (e.keyCode < 65 || e.keyCode > 90)) {
                e.preventDefault();
            }
        }
    }

    @HostListener('keypress', ['$event']) onKeyPress(event) {
        if (this.OnlyNumberWihtoutDecimel) {
            const key = event.which;
            if (!( key >= 48 && key <= 57) ) {
                event.preventDefault();
            }
        }

    }
}