JSFiddle - React, Tailwind, and code Playground

HTML

<script>
function check() {
    var valid = false;
    /*
        ...                    
    */
    return valid;
}
</script>

<form onsubmit="return check()" id="form">
    <input type="text" value="Dummy text" /><br />
    <input
        type="button"
        onclick="document.getElementById('form').onsubmit()"
        value="Test"
    />
</form>