Selecting features

HTML

<script src="http://openlayers.org/en/v3.0.0/build/ol.js"></script>
<link rel="stylesheet" href="http://openlayers.org/en/v3.0.0/css/ol.css">
<div id="map" class="map"></div>
<span id="msg"></span>

CSS

.map {
    width: 400px;
    height: 400px;
}

JavaScript

var view = new ol.View({
        center: [0, 0],
        zoom: 3
        })

var featureLayer = new ol.layer.Vector({
    source: new ol.source.Vector()
});

var box = new ol.interaction.DragBox({
    condition: ol.events.condition.shiftKeyOnly,
    style: new ol.style.Style({
        stroke: new ol.style.Stroke({
            color: '#ffcc33',
            width: 2
            })
        })
    })

var map = new ol.Map({
    target: 'map',
    layers: [
        new ol.layer.Tile({
            source: new ol.source.OSM()
        }),
        featureLayer,
    ],
    view: view,
    interactions: ol.interaction.defaults().extend([box])
    });

featureLayer.getSource().addFeatures([new ol.Feature(new ol.geom.Point([0, 0])), new ol.Feature(new ol.geom.Point([100000, 2000000])), new ol.Feature(new ol.geom.Point([500000, 1000000])), new ol.Feature(new ol.geom.Point([1000000, 65000])), new ol.Feature(new ol.geom.Point([-1000000, 2000000])), new ol.Feature(new ol.geom.Point([-100000, -2000000]))]);

box.on('boxend', function() {
    var featuresinBox = [];
    featureLayer.getSource().forEachFeature(function(e) {
        if (ol.extent.containsCoordinate(box.getGeometry().extent, e.getGeometry().getCoordinates())) {
            featuresinBox.push(e);
        }
    });
    document.getElementById("msg").innerHTML = featuresinBox.length;
});