regular expression leave only letters and spaces in javascript code example

Example: javascript regex only letters and spaces

//regex expression:
var reg_name_lastname = /^[a-zA-Z\s]*$/;

//Validation to the user_name input field
if(!reg_name_lastname.test($('#user_name').val())){ //
    alert("Correct your First Name: only letters and spaces.");
    valid = false;
}