Java Script Validation for UserName

Alphabets, numbers and space(' ') no special characters min 3 and max 20 characters.
Starts with an Alpahbet.

var ck_name = /^[A-Za-z][A-Za-z0-9 ]{3,20}$/;

functiuon test()
{
    ck_name.text(username) == true;
}