var user_api_key = "YOUR_USER_API_KEY";
var channel_id = 123456; // fallback channel ID
var read_api_key = 'YOUR_CHANNEL_READ_API_KEY';
if (window.parent) {
    var channel_id = window.parent.channel.channel.id;
    $.ajax({
        url: "https://api.thingspeak.com/channels.json",
        dataType: 'json',
        async: false,
        data: { 'api_key': user_api_key },
        success: function(data) {
            if (data) {
                $.each( data, function( key, channel ) {
                    if (channel.id == channel_id) {
                        $.each( channel.api_keys, function( key, api_key_data ) {
                            if (api_key_data.write_flag == false) {
                                read_api_key = api_key_data.api_key;
                                return false; // break out of loop
                            }
                        });
                    }
                });
            }
        }
    });
}