Question

How to test input Field Validate a comma exists in a input field ?

Answer 1

var value = document.getElementById('id-of-the-form-field').value 
// or: var value = document.getElementsByName('name-of-the-form-field')[0].value

if(value.indexOf(',') > -1) {
    // value contains a comma
}

If this is not what you want, you have to give more details.

Reference: .indexOf()