How to Redirect PHP form with Javascript depending on echo

You don't need javascript to achive this you can use pure php. You can use error checking if a field is empty in the form as follows

validate.php

if(isset($_POST['submit'])){
if (empty($_POST["email"])) {
    $emailErr = "Email is required";
        } else {
            $email = test_input($_POST["email"]);
            // check if e-mail address is well-formed
            if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
                 $emailErr = "Invalid email format"; 
            }
     }
if (empty($_POST["name"])) {
            $nameErr = "Name is required";
        } else {
            $name = test_input($_POST["name"]);
}

if (isset( $nameErr) ||  isset($emailErr){
     // you have a error
    }

else {
    $to = "[email protected]";
    $name = Trim(stripslashes($_POST['name']));
    $email = Trim(stripslashes($_POST['email']));
    $message = Trim(stripslashes($_POST['message']));
    $subject = "New Client Call";
    ....

This will check if "email" field is empty if it is it will promp a error "Email is required"

And then in your html you add the error

<form class="form-horizontal" action="validate.php" method="post">
    <label for="email">Email: </label>
    <input type="text" class="form-control input-sm" name="email">
    <span class="error">* <br><?php echo $emailErr;?></span>
    <input class="btn btn-info btn-lg" type="submit" name="submit" value="Submit">
    </form>

Hope that helps

You seem to be on the right path, before throwing the arguments into the the mailer I would say you can do more sanity checking to make sure all values are entered, this way you avoid trying to send emails that you know will fail, so you fail early and notify the user, you may also see the error message the mail function returns in case of failure to make it easy to rectify any other issues by using the erorr_get_last() method.

echo error_get_last()['message'];

Note: php mail does not verify the headers given, so you have to be 100% sure it's clean and there are no possibilities for the user to inject their own headers, so make sure you sanitize that too.

Then to do redirecting you can just directly replace the echo "success" and echo "error" calls with your javascript part.

So the script would finally look like this:

<?php

    $to = "[email protected]";
    $name = Trim(stripslashes($_POST['name']));
    $email = Trim(stripslashes($_POST['email']));
    $message = Trim(stripslashes($_POST['message']));
    $subject = "New Client Call";

    $missingFieldCount = 0;
    if(!isset($_POST['name'])) {
        echo "Error: Name requried";
        $missingFieldCount++;
    }
    if(!isset($_POST['email'])) {
        echo "Error: Email required";
        $missingFieldCount++;
    }
    if(!isset($_POST['message'])) {
        echo "Error: message required";
        $missingFieldCount++;
    }

    if($missingFieldcount > 0) {
        echo "Please fill in the missing $missingFieldcount fields, then submit again";
    } else {
        $body = 'name: ' .$name."\r\n";
        $body .= 'email: ' .$email."\r\n";          // Using .= to append instead of replace
        $body .= 'message: ' .$message."\r\n";

        $headers = "From:<$email>"; //Make sure $email is actually just an email address and not injected headers

        $success = mail($to, $subject, $body, $headears);

        if ($success) {
            $redirectPage = "successPage.html"
        } else {
            $redirectPage = "errorPage.html"
            echo "An error occured:";

            //Don't show this to the user, but log it to file instead
            //this is here only for demonstration
            echo error_get_last()['message'];
        }

        echo "<form action="$redirectPage" method="post" name="redirect" ></form>";
        echo "<script> document.forms['redirect'].submit()</script>";
    }
}
?>

Tnq Guys for your answers. finally i manged a perfect PHP form from all the information i get in this issue. no need Javascript to redirect TO 2 different pages: 1. Thank you page. 2. error page.

and the code is like this:

<?php
$name = Trim(stripslashes($_POST['name'])); 
$email = Trim(stripslashes($_POST['email'])); 
$message = Trim(stripslashes($_POST['message'])); 
$to = "[email protected]";
$subject = " New Client order ";
$errors = 0;


$body ="";
$body .="Name: ";
$body .=$name;
$body .="\n";
$body .="Email: ";
$body .=$email;
$body .="\n";
$body .="Message: ";
$body .=$message;
$body .="\n";



if(isset($_POST['submit'])) { // Checking null values in message.

    $name = $_POST["name"]; // Sender Name
    $email = $_POST["email"]; // Sender's email ID
    $message = $_POST["message"]; // Sender's Message


    if (empty($_POST["name"])){
        $nameError = "Name is required";
        $errors = 1;
    }
    if(!filter_var($_POST["email"], FILTER_VALIDATE_EMAIL))
    {
        $emailError = "Email is not valid";
        $errors = 1;
    }

    if (empty($_POST["message"])){
        $messageError = "Message is required";
        $errors = 1;
    }

}   
if($errors == 0){
    $successMessage = mail($to, $subject, $body, "From: <$email>");
}
    else {
         print "<meta http-equiv=\"refresh\" content=\"0;URL=error.html\">";
    }

if ($successMessage){
   print "<meta http-equiv=\"refresh\" content=\"0;URL=thanks.html\">";
}


?>