Functional monkey patching in javascript

patch-tools.js

// Remember: With great power comes great responsibility

/* Runtime Hooks */

// Run patcher fn before the original function invocation
// aArgs - array / node list of arguments
function before(fn){
  return function(original){
    fn.apply(this, aArgs)
    return original.apply(this, aArgs)
  }
}

// Run patcher fn after the original function invocation
// aArgs - array / node list of arguments
function after(fn) { 
  return function(original) {
    return function() {
      var value = original.apply(this, aArgs)
      fn.apply(this, aArgs)
      return value
    }
  }
}

// Calls patcher fn accepting original fn invocation as the only argument
// aArgs - array / node list of arguments
function compose(fn){
  return function(original){
    return function(){
      return fn.call(this, original.apply(this, aArgs))
    }
  }
}

/* Utils */

// Replace an internal method of a class instance
// object - an instance of the class to override (obj)
// method - the method's name (str)
// callback -  consume the original method and return something else (fn)
function override(object, method, callback) {
  object[method] = callback(object[method])
}