javascript - Why doesn't underscore validate its functions? -

particularly in implementation of _.each. seems simple typeof iterator === 'function' trick. possibly or obj == null check.

  // cornerstone, `each` implementation, aka `foreach`.   // handles objects built-in `foreach`, arrays, , raw objects.   // delegates **ecmascript 5**'s native `foreach` if available.   var each = _.each = _.foreach = function(obj, iterator, context) {     if (obj == null) return obj;     if (nativeforeach && obj.foreach === nativeforeach) {       obj.foreach(iterator, context);     } else if (obj.length === +obj.length) {       (var = 0, length = obj.length; < length; i++) {         if (iterator.call(context, obj[i], i, obj) === breaker) return;       }     } else {       var keys = _.keys(obj);       (var = 0, length = keys.length; < length; i++) {         if (iterator.call(context, obj[keys[i]], keys[i], obj) === breaker) return;       }     }     return obj;   }; 

there no need validation. if input function incorrect, caused programming error , should treated such blowing up.