validation of input text field in html using javascript

Answer 1

    First Name:  

     

    

  

    1.word should be atleast 5 letter

    2.No space should be encountered

    3.No numbers and special characters allowed

    4.letters can be repeated upto 3(eg: aa is allowed aaa is not allowed)
  
  Validate now


validateForm = function () {
    return checkName();
}

function checkName() {
    var x = document.myForm;
    var input = x.name.value;
    var errMsgHolder = document.getElementById('nameErrMsg');
    if (input.length < 5) {
        errMsgHolder.innerHTML =
            'Please enter a name with at least 5 letters';
        return false;
    } else if (!(/^\S{3,}$/.test(input))) {
        errMsgHolder.innerHTML =
            'Name cannot contain whitespace';
        return false;
    }else if(!(/^[a-zA-Z]+$/.test(input)))
    {
        errMsgHolder.innerHTML=
                'Only alphabets allowed'
    }
    else if(!(/^(?:(\w)(?!\1\1))+$/.test(input)))
    {
        errMsgHolder.innerHTML=
                'per 3 alphabets allowed'
    }
    else {
        errMsgHolder.innerHTML = '';
        return undefined;
    }       

}

.error {
color: #E00000;
 }