<form action="iframe.php" target="my_iframe" method="post">
   <label for="text">Name:</label>
   <input type="text" name="full_name">
   <label for="text">Email:</label>
   <input type="text" name="email">
   <input type="submit" value="post">
</form>
<iframe name="my_iframe" src="iframe.php"></iframe>

www.apphp.com/index.php?snippet=html-post-data-into-iframe

To send data into iFrame you don't need JavaScript or anything. You just have the form's target attribute match the iframe's name attribute. The outer page doesn't even reload. Copy this code and test it.

Post Data to iFrame with HTML Only

html, post

HTML