var从php文件到带有ajax的js文件

In my main.php file in the main root i'm using:

$isWebView = false;
    if((strpos($_SERVER['HTTP_USER_AGENT'], 'Mobile/') !== false) && (strpos($_SERVER['HTTP_USER_AGENT'], 'Safari/') == false)) :
    $isWebView = true;
    elseif(isset($_SERVER['HTTP_X_REQUESTED_WITH'])) :
    $isWebView = true;
    endif;

echo json_encode($isWebView);

to check if is webview or browser and i save result as a boolean in the $isWebView var.

now i'm trying to load that result in my main.js file inside scripts folder like below but it doesn't work, why? i get error data is not defined.

$.ajax({
    url: 'main.php',
    type: 'POST',
    dataType: 'json',
    data: data,
    success: function(data){
        console.log(data);
    }
  });

Define the value of data inside the ajax request call

$.ajax({
    url: 'main.php',
    type: 'POST',
    dataType: 'json',
    data: {},
    success: function(result){
        try{
          JSON.parse(result);
          console.log(result.isWebView)
        } catch (err) {
          console.log("non json respone");
        }
    }
  });

Inside the php

$response = [];

$response['isWebView'] = false;

if ( (strpos($_SERVER['HTTP_USER_AGENT'], 'Mobile/') !== false) && (strpos($_SERVER['HTTP_USER_AGENT'], 'Safari/') == false) ) {
    $response['isWebView'] = true;
} elseif( isset($_SERVER['HTTP_X_REQUESTED_WITH']) ) {
    $response['isWebView'] = true;
}

echo json_encode($response);