Blender export to Three.js

var loader = new THREE.JSONLoader(true);
loader.load({
    model: "model.js",
    callback: function(geometry) {
        mesh = new THREE.Mesh(geometry,new THREE.MeshFaceMaterial);
        mesh.position.set(0,0,0);
        mesh.scale.set(20,20,20);
        scene.add(mesh);
        renderer.render(scene, camera);
    }
});

Is a basic json loader for THREE.JS; you also need to look into:

How to set up the canvas, scene, lights and camera (if you haven't already and aren't using the blender ones)

morphTargets (if you are animating)

materials (if you want to tweak)

The easiest way I found after many searches and trial and error was Three.ColladaLoader. Place your .dae files in a folder titled models in your /root directory. I found the Blender JSON exporter less reliable. Call the PinaCollada function from within the init() function, somthing like this:

function init(){
    scene = new THREE.scene;
    ...
    var object1 = new PinaCollada('model1', 1);
    scene.add(object1); 
    var object2 = new PinaCollada('model2', 2);
    scene.add(object2); 
    ...
}

function PinaCollada(modelname, scale) {
    var loader = new THREE.ColladaLoader();
    var localObject;
    loader.options.convertUpAxis = true;
    loader.load( 'models/'+modelname+'.dae', function colladaReady( collada ) {
        localObject = collada.scene;
        localObject.scale.x = localObject.scale.y = localObject.scale.z = scale;
        localObject.updateMatrix();
    } );
    return localObject;
}

you need the threejs blender exporter: read this