Q:

Uncaught TypeError: Cannot read property 'ajax' of undefined When I'm trying to send data to url

I have created a form to get feedback from user, I’m simply trying to send form data to url, but I’m getting this error:

Uncaught TypeError: Cannot read property 'ajax' of undefined

function sendData(){
    $.ajax({
        url: "www.yashkjhsah.php",
        type: "POST",
        async: true,
        data: $(".contacts_form").serialize(),
        dataType: "html",
        success: function(data) 
        {
            alert(data);
            if(data!="Error in Insert Query!")
            {
                alert("Thank you for Enquiry we will send answer in your Mail.");
            }
            else
            {
                alert("Error while saving the data");
            }
        }
    });
}

A:

The error message says that jQuery is not define.
You must include jQuery before doing anything with $.ajax
Put this line in the html page before your script :
<script src="https://code.jquery.com/jquery-1.11.3.min.js"></script>

