var value = false;

function gettersetter(bool){
        // _args = array with function arguments
        var _args = Array.prototype.slice.call(arguments);
        if(_args.length == 0){
            // if no arguments -> define get method
            return value;
        } else if(_args.length > 0){
            value = bool;
        }
    }

How to use it:
// getter
var newValue = gettersetter();
// setter
gettersetter(true);

var value = false;

function gettersetter(bool){
        // _args = array with function arguments
        var _args = Array.prototype.slice.call(arguments);
        if(_args.length == 0){
            // if no arguments -> define get method
            return value;
        } else if(_args.length > 0){
            value = bool;
        }
    }

This example can be extended to include a more general object. here I get or set a single value

Simple getter and setter method depending on number of arguments

JavaScript