How can I overload operators in Unity Javascript

I tried using this code to modify the [] operator:

static operator [] ( iRow:int ):float { return parseFloat(m[iRow]); }

it did not work but in the unity reference, there were some operator overloads defined in the same way.

There isn't a [] operator.

In c# you can created indexers (the things arrays and hashtables use) like this:

public string this[string key]
    return internalStringDictionary[key];

but i don't think js has the relevant syntax to express it