JSFiddle - React, Tailwind, and code Playground

HTML

<form name="myForm">
        <div class="input-group">
            <input type="text" class="form-control" maxlength="3" name="num" id="num" /> 
            <span class="input-group-btn">
                <button class="btn btn-primary" type="button" onclick="processInp()">GO</button>
            </span>
        </div><!-- /input-group -->
        </form>

JavaScript

window.processInp = function () {
var x = parseInt(document.querySelector('input[name="num"]').value);
if (!x) {
alert("NaN");
return false
} else if (x > 480) {
alert("Overflow!");
return false
}
window.open("../files/" + x + '.html');
return true
}