How to write THIS jquery ajax code in PLAIN js to send to PHP?

How to write THIS jquery ajax code in PLAIN js to send to PHP?

I've been using jquery ajax all over my website to return data from PHP as json_encode(). And works fine in Firefox, but Chrome, Safari and mobile browsers make the users ajax requests like 10 times slower. I do receive a TON of JSON's coming from PHP back to my jquery success.

I've been trying to replicate this jquery ajax code to receive it in PHP as I receive it with jquery, as a $_POST superglobal for each JSON element.. I've tried a lot of different ways with plain JS but couldn't get it to work AT ALL. I hope I could get some help here. Thanks!

jquery ajax: 
$.ajax({ dataType: 'JSON', data: { string_1:string_1, string_2:string_2 }, type: 'POST', url:url, success: function(data) { $('.div_1').html(data.string_1); $('.div_2').html(data.string_2); } });



PHP (I receive the above code as the following):

$string_1 = $_POST['string_1']; $string_2 = $_POST['string_2']; $json_arr = array( 'string_1'=>$string_1, 'string_2'=>$string_2 ); echo json_encode($json_arr);