XMLHttpRequest to Post HTML Form

The POST string format is the following:

name=value&name2=value2&name3=value3


So you have to grab all names, their values and put them into that format. You can either iterate all input elements or get specific ones by calling document.getElementById().

Warning: You have to use encodeURIComponent() for all names and especially for the values so that possible & contained in the strings do not break the format.

Example:

var input = document.getElementById("my-input-id");
var inputData = encodeURIComponent(input.value);

request.send("action=dosomething&" + input.name + "=" + inputData);

Another far simpler option would be to use FormData objects. Such an object can hold name and value pairs.

Luckily, we can construct a FormData object from an existing form and we can send it it directly to XMLHttpRequest's method send():

var formData = new FormData( document.getElementById("my-form-id") );
xhr.send(formData);

The ComFreek's answer is correct but a complete example is missing.

Therefore I have wrote an extremely simplified working snippet:

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="X-UA-Compatible" content="IE=Edge, chrome=1"/>

<script>
"use strict";
function submitForm(oFormElement)
{
  var xhr = new XMLHttpRequest();
  xhr.onload = function(){ alert(xhr.responseText); }
  xhr.open(oFormElement.method, oFormElement.getAttribute("action"));
  xhr.send(new FormData(oFormElement));
  return false;
}
</script>
</head>

<body>
<form method="POST"
      action="post-handler.php"
      onsubmit="return submitForm(this);" >
   <input type="text"   value="previousValue" name="name"/>
   <input type="submit" value="Update"/>
</form>
</body>
</html>

This snippet is basic and cannot use GET. I have been inspired from the excellent Mozilla Documentation. Have a deeper read of this MDN documentation to do more. See also this answer using formAction.

Tags:

Javascript

Forms

Ajax

Http Post

Xmlhttprequest

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