Page auto refreshinng after fetch, when using “move_uploaded-file()” method in PHP

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Javascript

PHP

I send files via fetch and uploading them in PHP with move_uploaded_file() method.The problem is when i use move_uploaded_file() method page automatically refresh and even when i upload multiple files just first one uploading and refresh page again.
Desired outcome is the file to be uploaded to the folder and current page not be refreshed. By the way i working on localhost.

What I have tried:

PHP Codes

if($img['error'] == 0 && $img['size'] > 0){
        if (!is_dir('naber')) {
            mkdir('naber', 0777, true);
        }
        
        $allowedExts = array("gif", "jpeg", "jpg", "png");
        $extension = pathinfo($img['name'])['extension'];
        if(!(in_array($extension, $allowedExts))){
            $result['status'] = false;
            $result['errmessage'] = 'Image type is invalid';
            exit(json_encode($result));
        }
        $target_path = 'naber/';
        $filename = time().'.'. strtolower($extension);
        $full_path = $target_path."".$filename;
        if(move_uploaded_file($img['tmp_name'], $full_path)){
            $result['status'] = true;
            $result['message'] = 'Image added successfully!';
        }else{
            $result['status'] = false;
            $result['errmessage'] = 'Image type is invalid';
            exit(json_encode($result));
        }
    }
    exit(json_encode($result));

Javascript codes :

if(document.querySelector('#submit')) document.querySelector('#submit').addEventListener('click', (e) =>{
    e.preventDefault();
    ...
    fd = new FormData();
    Array.from(document.querySelectorAll('.test')).some((t) => {
        .......
                tests['test'+i]['img'] = t.querySelector('.input-ifile').files[0];
                fd.append('test'+i+'-img',tests['test'+i]['img']);
        .......
    fetch('handlers/handler.php', { method: 'POST' , body: fd})
    .then(function (response) {
        return response.text();
    })
    .then(function (body) {
        console.log(body)
        return false;
    });
})