I think the easy way to do this would be:

<input type="text" onkeypress='return event.charCode >= 48 && event.charCode <= 57' />

But the problem comes up when you paste some text then HTML5's number type input may be a better choice:

<input type="number" />

BTW you can find better suggestions if you search the SO like this.

Numbers are 48 through 57, so...

$(document).keypress(function (e) {
    var key = e.keyCode || e.charCode;
    if (key >= 48 && key <= 57) {
        alert('You pressed ' + (key - 48));
    }
});

See demo

The first character is unrestricted because you have nested keypress handlers. Try this:

$('.Number').keypress(function (event) {
    var keycode = event.which;
    if (!(event.shiftKey == false && (keycode == 46 || keycode == 8 || keycode == 37 || keycode == 39 || (keycode >= 48 && keycode <= 57)))) {
        event.preventDefault();
    }
});

Use event.key to get the actual value. To check if integer, just use isFinite

Copyinput.addEventListener("keydown", function(event) {
    const isNumber = isFinite(event.key) && event.key !== ' ';
});

Other option:

Copyconst isNumber = /^[0-9]$/i.test(event.key)

An easier HTML solution would be to use the number type input. It restricts to only numbers (kind of).

Copy<input type="number">

Either way, you should clean all user input with:

Copystring.replace(/[^0-9]/g,'');

Options:

1. Uisng event.which: It returns numeric value but it is deprecated.
2. Your idea of creating map is cool. To create the map, instead of using "event.key", use "event.code".

EVENT.CODE is your life saver.

Simple way to check that enter value is numeric is:

var checknumber = $('#textbox_id').val();

    if(jQuery.isNumeric(checknumber) == false){
        alert('Please enter numeric value');
        $('#special_price').focus();
        return;
    }