Created
January 11, 2010 11:09
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// 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 |
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