Передача массива из php в js

// Предположим в них ($idp, $p) находятся массивы... 
var jj = '{"idp":["soething","other","else"],"p":["sss","ddd","hhh"]}'; 
 
// In case you have JSON and not string you don't have to parse it... 
// var jj = {"idp":["soething","other","else"],"p":["sss","ddd","hhh"]};  
 
$.post("https://jsonplaceholder.typicode.com/posts", { 
    "dt": "something" 
  }, 
  function(arr) { 
    arr = $.parseJSON(jj); // <--- No need to do this in JSON case 
 
    // Keys are names idp and p 
    var idp = arr.idp; //arr[0]; <--- No number value key 
    var p = arr.p; //arr[1]; <--- No number value key 
    //---------------------------------------------------------------- 
 
    console.log(arr); 
    console.log(idp + ' | ' + p); 
 
  });

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>