JSFiddle - React, Tailwind, and code Playground
HTML
<input type="text" id="idtelf" value="123456789">
JavaScript
numberValidate("idtelf")
function numberValidate(idtelf){
var input = document.getElementById('idtelf');
var number = parseInt(input.value).toString();
var myString = number.toString().replace(/\D/g,'');
if(number.length ==9 && number.length == myString.toString().length)
{
alert( "Correct");
}
else {
alert( "Enter a valid number");
}
};