How to validate a form in jquery without using jQuery plugin Validate?

Loop through each input element in the form, and check if it has a value. If not append the error message to a string which you later alert out if valid is false.

$('#submit').on('click', function() {
var valid = true,
message = '';

$('form input').each(function() {
var $this = $(this);

if(!$this.val()) {
var inputName = $this.attr('name');
valid = false;
message += 'Please enter your ' + inputName + '\n';
}
});

if(!valid) {
alert(message);
}
});