Check if a variable is of function type

Question

Suppose I have any variable, which is defined as follows:

var a = function() {/* Statements */};

I want a function which checks if the type

Answer 1

Underscore.js uses a more elaborate but highly performant test:

_.isFunction = function(obj) {
  return !!(obj && obj.constructor && obj.call && obj.apply);
};

See: http://jsperf.com/alternative-isfunction-implementations

EDIT: updated tests suggest that typeof might be faster, see http://jsperf.com/alternative-isfunction-implementations/4