Loading large values of data from php to javascript?

I read this question php array loading into javascript to see what I can do to load a large amount of data from PHP to Javascript, it seems I may have implemented it wrong. Javascript processes and formats the data after it comes in from PHP which loads the data from a database, the data is placed into the client-side session storage so that the data can be worked with by each page. (If there is a better way to do this please let me know).

This is in one .php file.

<?php

session_start();

require_once 'classes/Membership.php';

$membership = new Membership();

$confirmation = $membership->confirm_membership();

if ($confirmation){

    $data = $membership->get_data("assump");

    echo '<script>var data = '.json_encode($data) .';</script>';

}

?>

This is in a separate .js file

function loadData(){

    // All sessionStorage can be accessed by any javascript file

    for(var i = 0; i < data.length; i++){

        sessionStorage.setItem("assump" + i, data[i]);

    }

}

However no values are being loaded. Is this even possible to do?

EDIT: I moved the javascript into the .php file where var data was being created from the php script at the top of the file, I placed the function loadData() into a script tag after the body tag in the html.