BuggyClass.js

// Common JavaScript error for parameter "shortcuts".

// Be careful when you do this shortcut to assign default values!
function BuggyClass(param1, param2,param3) {
   this.param1 = param1 || "defaultValue"
   this.param2 = param2 || true;
   this.param3 = param3 || -1;

   this.input = param1 + ".." + param2; 
   this.derived = this.param1 + ".." + this.param2; 
   this.same = this.derived == this.input; // should always be true, right?

}
BuggyClass.prototype.unexpected = function() {
   var res = [];
   for (attr in this) { 
       var t = typeof(this[attr]);
       if (t != "function" && t != "undefined") res.push(attr + "=" + this[attr]);
   }
   return res.join("\n")
}
BuggyClass.prototype.toString = BuggyClass.prototype.unexpected;

var show = self.consle ? console.log : function(msg) { alert(msg); }

var bugsMeDefault = new BuggyClass(null);

// This is buggy:
var bugsme = new BuggyClass("ok", false,0);


///// May not get what you expect!!!

var results = [
bugsMeDefault,
bugsme.unexpected(),
bugsme.param1, 
bugsme.param2 == false,
bugsme.param3 == 0,
].join("\n\n");

show(results);


// Questions: how do you set param2 to false in the constructor?
// Answer: not easily!!! 
// See also:   http://gist.github.com/274880

// How can we fix this class?
// See answers in BuggyClassFixed.js Gist
// http://gist.github.com/274169