monkey-patch.js

// Original method
var object = {
  method: function (x, y) {
    return x+y;
  }
}

// Add operations before or after!
object.method = (function (original) {
  return function (x, y) {

    // before
    // we could here modify "arguments" to alter original input
    console.log(x, '+', y, '?');
    
    // execute
    var result = original.apply(this, arguments);
    
    // after
    // we could here work on result to alter original output
    console.log('=', result);
    
    // aaaand the result
    return result;
  }
})(object.method);