oop.js

var MyClass = function(options) {

    /* create a private variable */
    privateOpt = options;

    /* create a public variable*/
    this.opt = options;

    /* to access this variable into the method */
    var that = this;

    if (typeof this.opt === 'string' || this.opt === '') {
        return;
    }

    /* undescore for convention */
    var _init = function() {
        return that.opt.light;
    };

    /* privileged method */
    this.incLight = function() {
        that.opt.light += 0.1;
        that.opt.dark -= 0.1;
        return that.opt.light;
    };


    _init();


};
var test = new MyClass({
    light: 0.5,
    dark: 0.5
});

document.write(test.privateOpt); /* return undefined */

document.write(test.opt); /* return our options value */

document.write(test._init); /* return undefined */

document.write(test.incLight()); /* return the neww value of the light after incrementing */

document.write(test.opt.dark); /* return the neww value of the dark */​