PHP code part of Form Validation using Ajax

Return a consistent JSON validation response

Use one response shape for success and failure so the browser does not have to parse custom text formats.

<?php
header('Content-Type: application/json; charset=utf-8');

$name = trim($_POST['name'] ?? '');
$errors = [];

if (mb_strlen($name) < 3) {
    $errors['name'] = 'Enter at least 3 characters.';
}

echo json_encode([
    'ok' => $errors === [],
    'errors' => $errors
]);
?>

Current practice: keep client-side validation for user experience, but always repeat validation on the server. For database input, use PDO or MySQLi prepared statements.

Current approach first; the original XMLHttpRequest/AJAX examples below are retained and cleaned up for continued learning and legacy maintenance.

In the first part of form validation we have seen how the Ajax form and the functions we have used to collect data from forms and then process it to handover to PHP file by using POST method. After getting the data we will write PHP code to validate the data and generate the message.

We have started with collecting the data, as we have used POST method of form submission so we used same technique to collect all four variables used in the form.

@$fname=$_POST['fname'];
@$sex=$_POST['sex'];
@$month=$_POST['month'];
@$agree=$_POST['agree'];

We set a flag to status 'OK' and at the end we will see if the $status_form is changed or not, if any of the validation fails then this status will change to NOTOK. We will also crate a variable to store the message and at the beginning it is kept blank.

$status_form = "OK";// Set a flag to check
$msg=""; // Message variable

$row=array("t1"=>"T","r1"=>"T","r2"=>"T","s1"=>"T","c1"=>"T","msg"=>"","status_form"=>"OK");

We have created one array with all the element status setting to T or validation is passed. As we check one by one element , we will change the status to false and add failure message to it.
Now we will start with checking the data which as come to us as fname for First name. We have set a validation check as it must me minimum 3 char in length. You can change your validation checking as per your requirement. It can be alphanumeric or it can be only alphabets or you can add maximum length to this. We have used strlen function to check the length of the entered data.

if(strlen($fname) < 3){
$row["status_form"]="NOTOK";
$row["t1"]="F";
$msg .= "Your Name must be more than 3 char  length<br>";
}

See that if the valdation is not OK then we are changing the $status_form and the message we are adding the respective elements of the array Similar way we have checked that the user has selected one of the two radio button by checking the variable sex. User must select one of the month so we have checked the variable $month. Finally we can check the status of the checkbox by checking its value is set to yes or not. If all the validations passed then the status of variable $status is checked ( OK or NOTOK) and output is given in green color font or in red color font.
demo of PHP Ajax form validation
This is a simple example on how to validate the form data using Ajax and PHP. But this is not complete code. We know after validation if the data is OK then we need to send the status message back to form. Now we can reset the form or we can redirect the page to another page with thank you message. How to do that ? Here so far we have seen how to send back a single line of message to main page , now we need to send another data saying the status of the validation. This we will learn in next part.

Download the code of this demo

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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Return Server-side Validation Results as JSON

Return a consistent JSON validation response

Subhendu Mohapatra