jQuery AJAX response type

If you are getting a string returned from your AJAX call, you need to add dataType: "json". This will make jQuery parse the response as JSON, if possible.

$(document).ready( function() {
    $("#user-btn").click(function() {
        $.ajax({
            type: "GET",
            url: "../php/client/json.php",
            data: {
                type: "users"
            },
            dataType: "json"
        }).done(function( response ) {
            ...
        });
});

Are you sure your ich.user method expects an array of users and not just a single user object?

Try the option dataType: "json" for $.ajax.

Modify the click function:

$("#user-btn").click(function () {
    $.ajax({
        type: "GET",
        url: "../php/client/json.php",
        data: {
            type: "users"
        },
        dataType: 'json',
        success: function (data) {
            // Your code...
        },
        error: function (xhr, textStatus, errorThrown) {
            alert(textStatus);
        }
    });
});