使用隐藏的iFrame提交PHP表单的成功/错误消息？

Question

I have a form on my site that I would like users to be able to submit without the page reloading. I found this answer which solved that part of it for me, but now I am trying to figure out how I would add success/error messaging to the form upon submit.

Here is my form code:

<iframe name="submit" style="display:none;"></iframe>
<form method="post" action="submit.php" target="submit">
    <input type="text" name="firstname" placeholder="First name" />
    <input type="text" name="lastname" placeholder="Last name" />
    <input type="text" name="email" placeholder="Email address" />
    <input type="submit" name="submit" value="" />  
</form>

How can I determine whether the form was submitted successfully or not and display a success or error message based on the result? Also open to other suggestions for submitting the form without the page reloading.

Answer 1

To clarify what other commenters are already saying or have said:

The source-code in your original post consists only of a vanilla "form submit," which will be dutifully carried out by the browser just as things were done when HTTP was first invented:   "the data will be submitted to the host, and whatever the host returns will be displayed as the 'next page.'" In this scenario, the role of the web-browser is totally passive.

Very commonly today, a technique called "AJAX" is used: instead of just "submitting the form" when a button is clicked, the submit-button causes a JavaScript subroutine to be run, and it (using an "Asynchronous HTTP Request" = "XHR") both submits the data to the host and intercepts the host's response. The role of (the JavaScript now being executed by) the web-browser is now active.

The host, in turn, now ordinarily does not return "displayable HTTP text." Knowing that it's being talked-to by another computer program, it instead sends that program something that can be very-easily consumed. The host typically sends "a data structure," which is ordinarily formatted in a format called "JSON."

... and, today, there are legions of great JavaScript libraries that can "make this a piece o' cake." (JQuery is only the most-popular one.)

Therefore, "surf over to some of these web sites, and take a look at their examples." (They not only supply the working demonstrations, for your amusement and amazement, but they show you on-the-spot exactly how it's done.)