Redefining the Array constructor in javascript
javascript
Solution
In both examples you're defining the variable `Array` to be a `function` that assigns `this` to `secrets`. It just so happens that there already exists a global object called `Array` that other JS in the page might or might not use as a `Constructor` to make arrays. If you pop into your console and re-assign Array to be something else, you might start getting errors from code that explicitly depends on `Array`. However, arrays made literally with `[]` continue to work just fine, and in fact, their `__proto__` still points to what was `Array.prototype`. So:
var arr1 = new Array('a','b','c');
// arr[0] -> 'a'
var arr2 = ['d','e','f'];
// arr[0] -> 'd'
var secrets;
Array = function() { secrets = this; };
var arr3 = new Array('g','h','i'); // nothing wrong here, because Array is a function
// arr3[0] -> undefined
// Array is just a function, you can't make arrays with new Array anymore
// and arr3 is just a function
var arr4 = ['j','k','l'];
// arr4[0] -> 'j'
// making array literals still works
as for `this`, nothing strange, still follows the rules of `this`. the fact that you're assigning a function to `Array` doesn't change how `this` behaves. so `this` points to the global object which in the browser is `window` unless you instantiate with `new` or use `call` or `apply`
the difference between both samples is the difference between a function expression and function declaration, see: What is the difference between a function expression vs declaration in Javascript?
Problem
Say I have the following code: ``` var secrets; Array = function() { secrets = this; }; ``` The author of the above sample says that the code is redefining the Array constructor. First, I am not sure what the `this` refers to. Can anyone please advise? Second: would the following code be equivalent? ``` var secrets; function Array() { secrets = this; } ``` By the way the above code is taken from the following article about a Json vulnerability: see here