JSFiddle - React, Tailwind, and code Playground

HTML

<form action="" method="post" onsubmit="return d(this);">
    <input type="hidden" id="flag" value="">
    <input type="text">
    <input type="submit" value="Ok" onclick="return d(this,event);">
</form>

JavaScript

function d(el,event){
    var flag = document.getElementById('flag');
    if(el.tagName.toLowerCase()=='input' 
       && event.clientX >0 
       && el.getAttribute('type').toLowerCase()=='submit') 
    {
        flag.value=el.value;
        return true;
    }  else if (el.tagName.toLowerCase()=='form') {
        if(flag.value!=""){
            return true;
        }; 
    }
    return false;            
}