Take the following class as an example:

```
function TestClass() {

  // public property
  this.testArray = [];

  // public function
  this.populateArray = function() {
    for (var y = 1; y <= 9; y++) {
      for (var x = 1; x <= 12; x++) {
        this.testArray[x + '-' + y] = true;
      }
    }
  };
}

```

When I call the `populateArray` method, it runs as expected, but it does not modify the `testArray` property.

I've tried pulling the method out and adding it via prototype, but that also does not work.

```
TestClass.prototype.populateArray = function() {};

```

The code that is calling the method is here:

```
var testClass = new TestClass();
testClass.populateArray();

```

Why is the method not populating the property?