array-listeners.js

array-listeners.js

Array.prototype.addEventListener = function(fn, cb) {
  if(!this.__eventListeners) {
    this.__eventListeners = {};
  }
 
  if(typeof(fn) !== 'string') {
    throw "Can't add event listener: 1st argument is not a string";
  }

  if(typeof(cb) !== 'function') {
    throw "Can't add event listener: 2nd argument is not a function";
  }

  if(!this[fn]) {
    throw "Can't add event listener: Array has no method " + fn + " defined";
  }

  if(!this.__eventListeners[fn]) {
    this.__eventListeners[fn] = [];
  }

  this.__eventListeners[fn].push(cb);
};

['push', 'pop', 'shift', 'unshift'].forEach(function(fn) {
  var old = Array.prototype[fn];
  Array.prototype[fn] = function() {
    var args = arguments, self = this;
    try {
      return old.apply(this, args);
    } finally {
      if(this.__eventListeners && this.__eventListeners[fn]) {
        this.__eventListeners[fn].forEach(function(cb) {
          cb.apply(self, args);
        });
      }
    }
  }
});

var a = [1,2,3];
a.addEventListener('push', function(i) {
  console.log('pushed ' + i + ' to ' + this);
});

a.addEventListener('pop', function(i) {
  console.log('popped from ' + this);
});

a.addEventListener('shift', function(i) {
  console.log('shifted ' + this);
});

a.addEventListener('unshift', function(i) {
  console.log('unshifted ' + i + ' from ' + this);
});

console.log(a.push(4));
console.log(a.pop());
console.log(a.push(5));
console.log(a.shift());
console.log(a.unshift(0));