gistfile1.js

Clazz = function(num) {
        var priv = num;
	this.pub = priv;
	that = this;
}

Clazz.prototype.outsider = function() {
	return priv;
}

c = new Clazz(6);
c.priv; // not defined
c.pub; // 6
c.outsider(); // not defined

gistfile2.js

Clazz = function(num) {
        priv = num; // removed the var from the definition
	this.pub = priv;
	that = this;
}

Clazz.prototype.outsider = function() {
	return priv;
}

c = new Clazz(6);
c.priv; // not defined
c.pub; // 6
c.outsider(); // 6!!!