Intercepts and wraps a method of a js object.

interceptMethod.js

// function interceptor

var interceptMethod = function(object, methodName, newMethodGen) {
  previousMethod = object[methodName]
  object[methodName] = newMethodGen(previousMethod)
}

// where newMethodGen is of the form
foo = {x: function() {console.log('foo.x')}}
interceptMethod(foo, 'x', function(f) {
  return function(n) {
    console.log('foo.x.pre.'+n)
    f.call(this)
    console.log('foo.x.post.'+n)
  }
})

foo.x()