Associative Javascript Array

I have an issue and this is not something that I have ever used before.

This is a snippet of the code.

//Defined at top of file
var ships_array = [];

//Function later on

    function refreshJSON(){
    $.getJSON("scripts/getJSON.php", function(json){

      if(json){
        $.each(shiplist,function(i,item){
            $.each(item,function(j,subitem){
                var mmsi = subitem['mmsi'];
                ships_array[mmsi].lat = subitem['lat'];
                ships_array[mmsi].lon = subitem['lon']; 

            });
        });
     } 

    });

    }

The error I a开发者_Python百科m getting is

ships_array[mmsi] is undefined [Break On This Error] ships_array[mmsi].lat = subitem['lat'];

Is this the right way to use an associative array? I have seen an example similar to this but I am going wrong somewhere! At the end of it I want an array of Google Maps markers!

you just need to initialize the value at the hash key first

var mmsi = subitem['mmsi'];
ships_array[mmsi] = ships_array[mmsi] || {};
ships_array[mmsi].lat = subitem['lat'];
ships_array[mmsi].lon = subitem['lon'];

You can change your code like this:

//Defined at top of file
var ships_array = [];

//Function later on

    function refreshJSON(){
    $.getJSON("scripts/getJSON.php", function(json){

      if(json){
        $.each(shiplist,function(i,item){
            $.each(item,function(j,subitem){
                var mmsi = subitem['mmsi'];
                ships_array[mmsi] = {lat: subitem['lat'], lon:subitem['lon']};
            });
        });
     } 

    });

    }