app/assets/javascripts/users/linkedin_validation.js
$( document ).ready(function() {
$('input#linkedin-field').on('keyup', validateLinkedIn);
});
function validateLinkedIn() {
if (this.value.match(/[^a-zA-Z0-9]/)) {
$(this).addClass('input-field-error')
$(this).siblings('#linkedin-hint').removeClass('hidden')
} else {
$(this).removeClass('input-field-error')
$(this).siblings('#linkedin-hint').addClass('hidden')
}
}