CodeIgniter - How to return Json response from controller

For CodeIgniter 4, you can use the built-in API Response Trait

Here's sample code for reference:

<?php namespace App\Controllers;

use CodeIgniter\API\ResponseTrait;

class Home extends BaseController
{
    use ResponseTrait;

    public function index()
    {
        $data = [
            'data' => 'value1',
            'data2' => 'value2',
        ];

        return $this->respond($data);
    }
}

return $this->output
            ->set_content_type('application/json')
            ->set_status_header(500)
            ->set_output(json_encode(array(
                    'text' => 'Error 500',
                    'type' => 'danger'
            )));

//do the edit in your javascript

$('.signinform').submit(function() { 
   $(this).ajaxSubmit({ 
       type : "POST",
       //set the data type
       dataType:'json',
       url: 'index.php/user/signin', // target element(s) to be updated with server response 
       cache : false,
       //check this in Firefox browser
       success : function(response){ console.log(response); alert(response)},
       error: onFailRegistered
   });        
   return false; 
}); 


//controller function

public function signin() {
    $arr = array('a' => 1, 'b' => 2, 'c' => 3, 'd' => 4, 'e' => 5);    

   //add the header here
    header('Content-Type: application/json');
    echo json_encode( $arr );
}

in my case , I'm using ci4 , I send response to clinet like this: e.g in App\Controllers\Category:setOrder my Category controller extends BaseController

  return $this->response->setJson(['msg'=>'update-success']);