Target all inputs

HTML

<label for="first">First</label><br>
<input type="number" min="0" />

<br><br>
    
<label for="Second">Second</label><br>
<input type="number" min="0" />

JavaScript

// Select your input element.
var numInput = document.querySelector('input');

// Listen for input event on numInput.
numInput.addEventListener('input', function(){
    // Let's match only digits.
    var num = this.value.match(/^\d+$/);
    if (num === null) {
        // If we have no match, value will be empty.
        this.value = "";
    }
}, false)