regex javascript number only

HTML

<input id="myInput" type="text" value="0" />

CSS

input {
    margin: 1em;
    padding: .5em;
}

JavaScript

(function() {
    var previousValue = document.getElementById('myInput').value;
   // var pattern = /^[0-9]$/;
    //var pattern = "-12345.50 €".replace(/[^\d.-]/g, '');
    var pattern = /[^\d-]/g;
    
    function validateInput(event) {
        event = event || window.event;
        var newValue = event.target.value || '';
        console.log(newValue.match(pattern));
        if (newValue.match(pattern)) {
            // Valid input; update previousValue:
            previousValue = newValue;
        } else {
            // Invalid input; reset field value:
            event.target.value = previousValue;
        }
    }
    
    document.getElementById('myInput').onkeyup = validateInput;
}());