JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" class="textfield" value="" id="textId" name=""  />

<div id ="result">

</div>

JavaScript

$(function(){
$('#textId').on('input',function(){
	console.log($(this).val())

  var regex = /^\+(?:[\d]*)$/ ;
    console.log($(this).val())
    var res = regex.test($(this).val());
    $('#result').text(regex.test($(this).val()))
});

})