Javascript Object Extension

Question

I am working with Leaflet for a map on my site. I want to build the layer switcher dynamically. The constructor takes an object, with key being name of the layer to display on map and value being the layer object itself. I am building the switcher dynamically from an array returned by AJAX. The problem I'm having is that I don't know how to get the value of an array object to be the key in my new object. My code looks like this:

$.ajax ({
    url: '...',
    data: { ... },
    dataType: 'json',
    success: function (data) {
        var overlayMaps = {};
        for (var i in data.elems) {
            var layer = new Layer (...);
            overlayMaps = $.extend ({}, overlayMaps, {data.elems[i].name : layer});
            map.addLayer (layer);
        }
        map.addControl (new L.Control.Layers (baseMaps, overlayMaps));
    }
});

My question is how to do line #9. data.elems[i].name doesn't want to work. I get this error missing : after property id, pointing right to the . after data. Any ideas?

What do you mean when you say it doesn't 'want to work'? Does that mean that is doesn't have a value or what? What do you see if you add data.elems[i] to your watch list in the debugger? — Vivian River
– Vivian River, Commented Apr 9, 2012 at 18:41
Object keys can only be strings. If you pass anything other than a string, it will be coerced to a string. — Matt Ball
– Matt Ball, Commented Apr 9, 2012 at 18:42
I mean I get this error missing : after property id, pointing right to the . after data. Sorry for not including that. — Nik
– Nik, Commented Apr 9, 2012 at 18:43
And that's my problem. How do I get the value to be a string? — Nik
– Nik, Commented Apr 9, 2012 at 18:43

Matt Ball · Accepted Answer · 2012-04-09 18:45:17Z

3

I think you're just looking for bracket notation. Instead of this:

overlayMaps = $.extend ({}, overlayMaps, {data.elems[i].name, layer});

you want this:

var opts = {};
opts[data.elems[i].name] = layer;
overlayMaps = $.extend ({}, overlayMaps, opts);

answered Apr 9, 2012 at 18:45

Matt Ball

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