Getter/setter on javascript array?

Question

Is there a way to get a get/set behaviour on an array? I imagine something like this:

var arr = ['one', 'two', 'three'];
var _arr = new Array();

for (var i = 0; i < arr.length; i++) {
    arr[i].__defineGetter__('value',
        function (index) {
            //Do something
            return _arr[index];
        });
    arr[i].__defineSetter__('value',
        function (index, val) {
            //Do something
            _arr[index] = val;
        });
}

Answer 1

Using Proxies, you can get the desired behavior:

var _arr = ['one', 'two', 'three'];

var accessCount = 0;
function doSomething() {
  accessCount++;
}

var arr = new Proxy(_arr, {
  get: function(target, name) {
    doSomething();
    return target[name];
  }
});

function print(value) {
  document.querySelector('pre').textContent += value + '
';
}

print(accessCount);      // 0
print(arr[0]);           // 'one'
print(arr[1]);           // 'two'
print(accessCount);      // 2
print(arr.length);       // 3
print(accessCount);      // 3
print(arr.constructor);  // 'function Array() { [native code] }'

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