OpenLayers why are there no features when converting non-zero Selected features to JSON

Question

Using OpenLayers with a Select interaction to select features, I'm attempting to convert the selected features to JSON for further processing within the select.on('select', ...) as per the code below.

select.on('select', function() {
     try {
         var json = new ol.format.GeoJSON().writeFeatures(select.getFeatures(), {});
         console.log(select.getFeatures().getLength());
         console.log(json);
         doStuffWithJSON(json);
     } catch(err) {
         console.log(err.message);
     }
});

However, the output from the two console.log() lines is:

2

{"type":"FeatureCollection","features":[]}

Ie, there are 2 features selected, but the GeoJSON includes no features.

What am I doing wrong here, and how I can I convert this to correct GeoJSON?

Answer 1

As @Mike commented...

select.getFeatures() returns an OpenLayers collection, writeFeatures() expects an array of features so: select.getFeatures().getArray()

Fo my code, this now works as expected:

select.on('select', function() {
     try {
         var json = new ol.format.GeoJSON().writeFeatures(select.getFeatures().getArray(), {});
         console.log(select.getFeatures().getLength());
         console.log(json);
         doStuffWithJSON(json);
     } catch(err) {
         console.log(err.message);
     }
});