JSFiddle - React, Tailwind, and code Playground

HTML

Please type text like example.com:
<input name="url" type="text" onblur="checkIt(this)" />

JavaScript

// Removes leading whitespaces
function LTrim(value)
{
    var re = /\s*((\S+\s*)*)/;
    return value.replace(re, "$1");
}

// Removes ending whitespaces
function RTrim(value)
{
    var re = /((\s*\S+)*)\s*/;
    return value.replace(re, "$1");
}

// Removes leading and ending whitespaces
function trim(value)
{
    return LTrim(RTrim(value));
}

function hasDomainTld(strAddress)
{ 
  var strUrlNow = trim(strAddress);
  if(strUrlNow.match(/[,\s]/))
  {
    return false;
  }
  var i, regex = new RegExp(); 
  regex.compile("[A-Za-z0-9\-_]+\\.[A-Za-z0-9\-_]+$"); 
  i = regex.test(strUrlNow);
  regex = null;
  return i;
} 

function checkIt(objInput)
{
  var val = objInput.value;
  if(val.match(/http:/i)) {
    return false;
  }
  else if (hasDomainTld(val)) {
    objInput.value = 'http://' + val;
  }
}