Thread:Jens Ingels/@comment-3974211-20141201111120/@comment-3271569-20141203124916

I don't believe I used a filter function in the original code. A variable in js can contain these types:
 * Undefined
 * Null
 * Boolean
 * Number
 * String
 * Symbol
 * Host object (provided by the JS environment)
 * Function object
 * Any other object

The result NaN is listed as number type (as false number).