Function Overwriting in JavaScript

gistfile1.js

// Initial "getLocation" implementation. Since we only need to test
// for Geolocation support once, we perform the initial test and then
// overwrite the "getLocation" implementation based on the results of
// the test.
var getLocation = function (success, fail, options)
{
    var geolocation = navigator.geolocation;

    if ( geolocation )
    {
        var _options = {
            enableHighAccuracy: true,
            timeout: 60000,
            maximumAge: 0
        };
        // Geolocation is supported, so we overwrite the implementation
        // to simply invoke "geolocation.getCurrentPosition" as there
        // is no need to perform the test again.
        getLocation = function (success, fail, options)
        {
            geolocation.getCurrentPosition (success, fail, options || _options);
        }
        getLocation (success, fail, options);
    }
    else
    {
        // Geolocation is not supported, so we overwrite the
        // implementation to simply return false (a real
        // implementation might provide a polyfill here...).
        getLocation = function ()
        {
            return false;
        }
    }
};