instance method Function#wrap

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Function#wrap(wrapper) → Function
  • wrapper (Function) – The function to use as a wrapper.

Returns a function "wrapped" around the original function.

Function#wrap distills the essence of aspect-oriented programming into a single method, letting you easily build on existing functions by specifying before and after behavior, transforming the return value, or even preventing the original function from being called.

The wraper function is called with this signature:

function wrapper(callOriginal[, args...])

...where callOriginal is a function that can be used to call the original (wrapped) function (or not, as appropriate). (callOriginal is not a direct reference to the original function, there's a layer of indirection in-between that sets up the proper context [this value] for it.)

// Wrap String#capitalize so it accepts an additional argument
String.prototype.capitalize = String.prototype.capitalize.wrap(
  function(callOriginal, eachWord) {
    if (eachWord && this.include(" ")) {
      // capitalize each word in the string
      return this.split(" ").invoke("capitalize").join(" ");
    } else {
      // proceed using the original function
      return callOriginal();
 "hello world".capitalize();
// -> "Hello world" (only the 'H' is capitalized)
"hello world".capitalize(true);
// -> "Hello World" (both 'H' and 'W' are capitalized)