PHP - $_POST
PHP $_POST
$_POST contains an array of variables received via the HTTP POST method.
There are two main ways to send variables via the HTTP Post method:
- HTML forms
- JavaScript HTTP requests
$_POST in HTML Forms
A HTML form submits information via the HTTP POST method if
the form's method attribute is set to "POST".
To demonstrate this, we start by creating a simple HTML form:
HTML Form
<html>
<body>
<form method="POST" action="demo_request.php">
Name: <input type="text" name="fname">
<input type="submit">
</form>
</body>
</html>
When a user clicks the submit button, the form data is sent to a PHP file specified in the
action attribute of the
<form> tag.
In the action file we can use the $_POST variable
to collect the value of the input field.
PHP file
$name = $_POST['fname'];
echo $name;
In the example below we have put the HTML form and PHP code in the same PHP file.
We have also added some extra lines for security.
Example
<html>
<body>
<form method="POST" action="<?php echo $_SERVER['PHP_SELF'];?>">
Name: <input type="text" name="fname">
<input type="submit">
</form>
<?php
if ($_SERVER["REQUEST_METHOD"] == "POST") {
$name = htmlspecialchars($_POST['fname']);
if (empty($name)) {
echo "Name is empty";
} else {
echo $name;
}
}
?>
</body>
</html>
$_POST in JavaScript HTTP Requests
When sending a HTTP request in JavaScript, you can specify that the HTTP method is POST.
To demonstrate this we start by creating a JavaScript function containing a HTTP request:
JavaScript function
function myfunction() {
const xhttp = new XMLHttpRequest();
xhttp.open("POST", "demo_phpfile.php");
xhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
xhttp.onload = function() {
document.getElementById("demo").innerHTML = this.responseText;
}
xhttp.send("fname=Mary");
}
}
The code above will:
- Intiate a HTTP request
- Set the HTTP method to POST
- Set a valid request header
- Create a function to execute when the request is done
- Send the HTTP request with a variable
fnameset toMary
Look at the function that will be executed when the request is done:
xhttp.onload = function() {
document.getElementById("demo").innerHTML = this.responseText;
}
It will try to write a response from the operation in a HTML element with
id="demo".
Let us make a HTML page with such element, and also a button that executes the function.
If we also add the the JavaScript, the page looks like this:
Example
How to post and receive data from a HTTP request:
<html>
<script>
function myfunction() {
const xhttp = new XMLHttpRequest();
xhttp.open("POST", "demo_ajax.php");
xhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
xhttp.onload = function() {
document.getElementById("demo").innerHTML = this.responseText;
}
xhttp.send("fname=Mary");
}
}
</script>
<body>
<button onclick="myfunction()">Click me!</button>
<h1 id="demo"></h1>
</body>
</html>
In the PHP file that receive this HTTP request (demo_ajax.php), we simply use the $_POST variable
to retrieve the fname variable, and writes it as a response.
PHP file
$name = $_POST['fname'];
echo $name;
