Related
There is a web online, library or something to detect old IE functions that are not compatible with Chrome/Firefox or just ES6?
Like: document.all, event.returnValue, etc
JsHint/Jslint are not detecting them as deprecated or incompatibles
It's not quite fair to say JSLint won't tell you about deprecated properties. Let me explain.
Recall first that JavaScript is a dynamic language. You can assign any property to [almost] any object. You could assign all to window in a browser context if you wanted just by saying window.all = "Muahahaha!!! I'm evil!!!". You could add .all to a string with...
var spam = "a string";
spam.all = "I'm still evil!!!"
Or, worse, some piece of code could have changed the prototype for String (or any other object type) somewhere outside of your file. Try this in a browser console:
String.prototype.all = String.prototype.all || "This is beyond evil.";
// 'This is beyond evil.'
var spam = "spam"
// undefined
spam.all
// 'This is beyond evil.'
So JSLint doesn't, by default, check for properties on objects by names. Especially for objects that could live outside of your file's context (because JSLint lints file-by-file), it simply can't know what's happened to an object's properties and identify what's valid and what isn't.
(That's what TypeScript is for, btw.)
Unless you tell JSLint how!! -- the JSLint property directive ftw
Or you can use the JSLint property directive, which does exactly what you want, if you're willing to do some work.
If you put the property directive at the top of your file, JSLint will show errors for any properties that are used by objects on the page that aren't in that list.
For instance, try this on the official JSLint.com page:
/*property
log
*/
/*jslint browser, devel */
function mySpam() {
var spam = document.all;
console.log(spam);
}
See how I'm using document.all but all isn't in the property directive? It's going to error for me.
1. Unregistered property name 'all'.
var spam = document.all;
You might be saying, "But it will take me FOREVER to get all the good properties from my 3000 line file I'm linting into that directive!!"
Not so! Here's a tip: Paste your file, even unlinted, into JSLint.com. It will create a property directive for you in its report.
Here's one I made from AngularJS' [sic] route.js in just a few seconds:
/*property
$$minErr, $evalAsync, $get, angularVersion, caseInsensitiveMatch, create,
defaultPrevented, eagerInstantiationEnabled, extend, info, isArray,
isDefined, isObject, isUndefined, length, module, noop, originalPath,
otherwise, preventDefault, provider, redirectTo, reload, reloadOnSearch,
reloadOnUrl, routes, run, substr, when
*/
Alphabetical, even.
Now just remove the ones you don't want and presto! You'll catch everything you need.
Is this a little tedious, and will it take a little massaging/training on files that use document properly? Yes, but, again, in a dynamic language, this is close to the best you can hope for with file-by-file linters.
NOTE: If this doesn't solve your issue, however imperfectly, that's when we need to see more of your files and hear more precisely what problem you're trying to solve in practice.
Intro
This topic has been the bane of many questions and answers on StackOverflow -and in many other tech-forums; however, most of them are specific to exact conditions and even worse: "over-all" security in script-injection prevention via dev-tools-console, or dev-tools-elements or even address-bar is said to be "impossible" to protect. This question is to address these issues and serve as current and historical reference as technology improves -or new/better methods are discovered to address browser security issues -specifically related to script-injection attacks.
Concerns
There are many ways to either extract -or manipulate information "on the fly"; specifically, it's very easy to intercept information gathered from input -to be transmitted to the server - regardless of SSL/TLS.
intercept example
Have a look here
Regardless of how "crude" it is, one can easily use the principle to fabricate a template to just copy+paste into an eval() in the browser console to do all kinds of nasty things such as:
console.log() intercepted information in transit via XHR
manipulate POST-data, changing user-references such as UUIDs
feed the target-server alternative GET (& post) request information to either relay (or gain) info by inspecting the JS-code, cookies and headers
This kind of attack "seems" trivial to the untrained eye, but when highly dynamic interfaces are in concern, then this quickly becomes a nightmare -waiting to be exploited.
We all know "you can't trust the front-end" and the server should be responsible for security; however - what about the privacy/security of our beloved visitors? Many people create "some quick app" in JavaScript and either do not know (or care) about the back-end security.
Securing the front-end as well as the back-end would prove formidable against an average attacker, and also lighten the server-load (in many cases).
Efforts
Both Google and Facebook have implemented some ways of mitigating these issues, and they work; so it is NOT "impossible", however, they are very specific to their respective platforms and to implement requires the use of entire frameworks plus a lot of work -only to cover the basics.
Regardless of how "ugly" some of these protection mechanisms may appear; the goal is to help (mitigate/prevent) security issues to some degree, making it difficult for an attacker. As everybody knows by now: "you cannot keep a hacker out, you can only discourage their efforts".
Tools & Requirements
The goal is to have a simple set of tools (functions):
these MUST be in plain (vanilla) javascript
together they should NOT exceed a few lines of code (at most 200)
they have to be immutable, preventing "re-capture" by an attacker
these MUST NOT clash with any (popular) JS frameworks, such as React, Angular, etc
does NOT have to be "pretty", but readable at least, "one-liners" welcome
cross-browser compatible, at least to a good percentile
Runtime Reflection / Introspection
This is a way to address some of these concerns, and I don't claim it's "the best" way (at all), it's an attempt.
If one could intercept some "exploitable" functions and methods and see if "the call" (per call) was made from the server that spawned it, or not, then this could prove useful as then we can see if the call came "from thin air" (dev-tools).
If this approach is to be taken, then first we need a function that grabs the call-stack and discard that which is not FUBU (for us by us). If the result of this function is empty, hazaa! - we did not make the call and we can proceed accordingly.
a word or two
In order to make this as short & simple as possible, the following code examples follow DRYKIS principles, which are:
don't repeat yourself, keep it simple
"less code" welcomes the adept
"too much code & comments" scare away everybody
if you can read code - go ahead and make it pretty
With that said, pardon my "short-hand", explanation will follow
first we need some constants and our stack-getter
const MAIN = window;
const VOID = (function(){}()); // paranoid
const HOST = `https://${location.host}`; // if not `https` then ... ?
const stak = function(x,a, e,s,r,h,o)
{
a=(a||''); e=(new Error('.')); s=e.stack.split('\n'); s.shift(); r=[]; h=HOSTPURL; o=['_fake_']; s.forEach((i)=>
{
if(i.indexOf(h)<0){return}; let p,c,f,l,q; q=1; p=i.trim().split(h); c=p[0].split('#').join('').split('at ').join('').trim();
c=c.split(' ')[0];if(!c){c='anon'}; o.forEach((y)=>{if(((c.indexOf(y)==0)||(c.indexOf('.'+y)>0))&&(a.indexOf(y)<0)){q=0}}); if(!q){return};
p=p[1].split(' '); f=p[0]; if(f.indexOf(':')>0){p=f.split(':'); f=p[0]}else{p=p.pop().split(':')}; if(f=='/'){return};
l=p[1]; r[r.length]=([c,f,l]).join(' ');
});
if(!isNaN(x*1)){return r[x]}; return r;
};
After cringing, bare in mind this was written "on the fly" as "proof of concept", yet tested and it works. Edit as you whish.
stak() - short explanation
the only 2 relevant arguments are the 1st 2, the rest is because .. laziness (short answer)
both arguments are optional
if the 1st arg x is a number then e.g. stack(0) returns the 1st item in the log, or undefined
if the 2nd arg a is either a string -or an array then e.g. stack(undefined, "anonymous") allows "anonymous" even though it was "omitted" in o
the rest of the code just parses the stack quickly, this should work in both webkit & gecko -based browsers (chrome & firefox)
the result is an array of strings, each string is a log-entry separated by a single space as function file line
if the domain-name is not found in a log-entry (part of filename before parsing) then it won't be in the result
by default it ignores filename / (exactly) so if you test this code, putting in a separate .js file will yield better results than in index.html (typically) -or whichever web-root mechanism is used
don't worry about _fake_ for now, it's in the jack function below
now we need some tools
bore() - get/set/rip some value of an object by string reference
const bore = function(o,k,v)
{
if(((typeof k)!='string')||(k.trim().length<1)){return}; // invalid
if(v===VOID){return (new Function("a",`return a.${k}`))(o)}; // get
if(v===null){(new Function("a",`delete a.${k}`))(o); return true}; // rip
(new Function("a","z",`a.${k}=z`))(o,v); return true; // set
};
bake() - shorthand to harden existing object properties (or define new ones)
const bake = function(o,k,v)
{
if(!o||!o.hasOwnProperty){return}; if(v==VOID){v=o[k]};
let c={enumerable:false,configurable:false,writable:false,value:v};
let r=true; try{Object.defineProperty(o,k,c);}catch(e){r=false};
return r;
};
bake & bore - rundown
These are failry self-explanatory, so, some quick examples should suffice
using bore to get a property: console.log(bore(window,"XMLHttpRequest.prototype.open"))
using bore to set a property: bore(window,"XMLHttpRequest.prototype.open",function(){return "foo"})
using bore to rip (destroy carelessly): bore(window,"XMLHttpRequest.prototype.open",null)
using bake to harden an existing property: bake(XMLHttpRequest.prototype,'open')
using bake to define a new (hard) property: bake(XMLHttpRequest.prototype,'bark',function(){return "woof!"})
intercepting functions and constructions
Now we can use all the above to our advantage as we devise a simple yet effective interceptor, by no means "perfect", but it should suffice; explanation follows:
const jack = function(k,v)
{
if(((typeof k)!='string')||!k.trim()){return}; // invalid reference
if(!!v&&((typeof v)!='function')){return}; // invalid callback func
if(!v){return this[k]}; // return existing definition, or undefined
if(k in this){this[k].list[(this[k].list.length)]=v; return}; //add
let h,n; h=k.split('.'); n=h.pop(); h=h.join('.'); // name & holder
this[k]={func:bore(MAIN,k),list:[v]}; // define new callback object
bore(MAIN,k,null); let f={[`_fake_${k}`]:function()
{
let r,j,a,z,q; j='_fake_'; r=stak(0,j); r=(r||'').split(' ')[0];
if(!r.startsWith(j)&&(r.indexOf(`.${j}`)<0)){fail(`:(`);return};
r=jack((r.split(j).pop())); a=([].slice.call(arguments));
for(let p in r.list)
{
if(!r.list.hasOwnProperty(p)||q){continue}; let i,x;
i=r.list[p].toString(); x=(new Function("y",`return {[y]:${i}}[y];`))(j);
q=x.apply(r,a); if(q==VOID){return}; if(!Array.isArray(q)){q=[q]};
z=r.func.apply(this,q);
};
return z;
}}[`_fake_${k}`];
bake(f,'name',`_fake_${k}`); bake((h?bore(MAIN,h):MAIN),n,f);
try{bore(MAIN,k).prototype=Object.create(this[k].func.prototype)}
catch(e){};
}.bind({});
jack() - explanation
it takes 2 arguments, the first as string (used to bore), the second is used as interceptor (function)
the first few comments explain a bit .. the "add" line simply adds another interceptor to the same reference
jack deposes an existing function, stows it away, then use "interceptor-functions" to replay arguments
the interceptors can either return undefined or a value, if no value is returned from any, the original function is not called
the first value returned by an interceptor is used as argument(s) to call the original and return is result to the caller/invoker
that fail(":(") is intentional; an error will be thrown if you don't have that function - only if the jack() failed.
Examples
Let's prevent eval from being used in the console -or address-bar
jack("eval",function(a){if(stak(0)){return a}; alert("having fun?")});
extensibility
If you want a DRY-er way to interface with jack, the following is tested and works well:
const hijack = function(l,f)
{
if(Array.isArray(l)){l.forEach((i)=>{jack(i,f)});return};
};
Now you can intercept in bulk, like this:
hijack(['eval','XMLHttpRequest.prototype.open'],function()
{if(stak(0)){return ([].slice.call(arguments))}; alert("gotcha!")});
A clever attacker may then use the Elements (dev-tool) to modify an attribute of some element, giving it some onclick event, then our interceptor won't catch that; however, we can use a mutation-observer and with that spy on "attribute changes". Upon attribute-change (or new-node) we can check if changes were made FUBU (or not) with our stak() check:
const watchDog=(new MutationObserver(function(l)
{
if(!stak(0)){alert("you again! :D");return};
}));
watchDog.observe(document.documentElement,{childList:true,subtree:true,attributes:true});
Conclusion
These were but a few ways of dealing with a bad problem; though I hope someone finds this useful, and please feel free to edit this answer, or post more (or alternative/better) ways of improving front-end security.
I have a very strange problem with javascript and easel js.
I am using the easel.js library and am already fairly far into the construction of a project using it.
I am attempting to have a 'class' (I know they aren't technically classes in javascript but I will use this terminology for lack of a better word) inherit the Shape class from easel js, and then have another class inherit that. So it would be something like this:
easeljs.Shape --> MenuButton --> BuildingButton
The code I am using looks like this:
BuildingButton.prototype = Object.create(MenuButton.prototype);
BuildingButton.prototype.constructor = BuildingButton;
function BuildingButton(){
MenuButton.call(this);
}
MenuButton.prototype = Object.create(createjs.Shape.prototype);
MenuButton.prototype.constructor = MenuButton;
function MenuButton(){
createjs.Shape.call(this);
}
The problem is that I get the following error with this code:
Uncaught TypeError: undefined is not a function
easeljs-0.7.1.combined.js:8439
(line 8439 is pointing to the initialize() function in the Shape() constructor).
now here's the strange thing. If I change the order of the definitions so that the sub class is defined second and not first, it works fine!
MenuButton.prototype = Object.create(createjs.Shape.prototype);
MenuButton.prototype.constructor = MenuButton;
function MenuButton(){
createjs.Shape.call(this);
}
BuildingButton.prototype = Object.create(MenuButton.prototype);
BuildingButton.prototype.constructor = BuildingButton;
function BuildingButton(){
MenuButton.call(this);
}
This is very confusing as I can't seem to figure out why on earth this is happening. I could just make sure I define them in the correct order and leave it be, but I have all my 'classes' in different source files which are then strung together by grunt, which does so alphabetically.
Also, I feel like I may have a big gap in my knowledge of javascript (or maybe easel.js I'm not sure what exactly is causing this behaviour).
Thanks in advance for your help and I hope the question makes sense!
MenuButton.prototype = Object.create(createjs.Shape.prototype);
…
BuildingButton.prototype = Object.create(MenuButton.prototype);
These two statements have a clear dependency and need to be executed in the correct order (for the function declarations the order is irrelevant if placed in the same scope/file, but if in different files they need to be loaded in the correct order obviously).
I have all my 'classes' in different source files which are then strung together by grunt, which does so alphabetically
That's not a good idea. You should use some build tool/script that allows the declaration of dependencies.
Read this to clear things out: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Inheritance_and_the_prototype_chain
In first example you try to inherit from nothing, since MenuButton.prototype is not yet defined. To make it work just add MenuButton.prototype = new createjs.Shape.prototype(instead of Object.create() wich shouldn't be used anymore) to instantiate it first before you can you use it. Your first code is like you are willing to eat a banana before having one.
I am converting tutorials for students (2nd language speakers, 9 to 12 yrs old) to access in an offline / intranet context. Hence the websites I would like them to use are unavailable.
I am trying to mimic the 'alter the code' style of tutorials for helping with JavaScript / HTML5 Canvas.
This works :
<canvas id="myCanvas" height="400px" width="400px"></canvas>
<script>
function update(){
eval(document.getElementById('demoScript').value);
}
var ctx = document.getElementById("myCanvas").getContext("2d");
</script>
<textarea id="demoScript">
ctx.fillRect(100,100,50,50);
</textarea>
<input type="button" value="update" onClick="update()">
... but everything I have read says eval() is a bad idea.
I can get the textarea content to pop-up in a div if I want, but I can't get it to pop-up in a script anywhere ... leaving me with just eval().
Options and recommendations for alternatives please ... or this is as good as it gets ?
This is an acceptable use for eval, because at worst a student will lock up their own browser with an infinite loop.
First of all, it's not a "bad idea" to use eval.
Second: anything that replaces eval will have the same "disadvantages" since it executes code. You'll have to execute code to do this. If you don't want to make your own interpreter (which is at least ten times worse and more vulnerable) you'll have to stick with eval or something similar.
Now what is the danger of it? Nothing else but the fact that it executes code. It's like telling someone that a hammer is dangerous because it hits hard - YES, and it's necessary when it gets to nailing something. Of course, a hammer can kill.
So,
Use eval,
...but sanitize the code it gets (= watch out for dangerous expressions, etc).
You can limit a lot of things for the user, like only one instruction per line, only double quotes, etc, to make it more controllable. Anything that's off the limit will be deleted. If no dangerous thing can be pushed thru the input, eval is harmless.
Options and recommendations for alternatives please ... or this is as good as it gets ?
I'd suggest using the Function constructor instead of eval. While in your simple example it may not make much difference, in other cases it may.
This will make the code evaluate in the global scope, so none of your local variables can be touched. It also allows JS engines to more easily optimize the local code. Using eval() can disable optimizations.
So to use the Function constructor, just pass the code to eval as the last argument. Since you have no parameters to define for the new function, it'll be the only argument.
var f = new Function("return " + document.getElementById("demoScript").value);
Then invoke the function.
f();
Notice that I concatenated a return statement into the provided code. This isn't required if you don't care about getting the returned value from the code your invoking, and should be removed if it might interfere with the provided code.
And of course, you can do this all in one line if you're only going to invoke it once.
new Function(document.getElementById("demoScript").value)();
You can get the value string from the textarea, split, validate and run it manually.
For a demonstration like this, where ctx is given, something like this should work
var ctx = document.getElementById("myCanvas").getContext("2d");
function update(){
var val = document.getElementById('demoScript').value,
fn = val.match(/\.(.*?)\(/),
arg = val.match(/\((.*?)\)/);
if (fn && fn.length > 0) {
if (arg && arg.length > 0) {
var args = arg[1].indexOf(',') != -1 ? arg[1].split(',') : [arg[1]];
ctx[fn[1]].apply(ctx, args);
}else{
ctx[fn[1]]();
}
}
}
FIDDLE
You could do
var fn = document.getElementById("demoScript").value;
window[fn]();
I am have some JavaScript functions that run on both the client (browser) and the server (within a Java Rhino context). These are small functions - basically little validators that are well defined and don't rely upon globals or closures - self-contained and portable.
Here's an example:
function validPhoneFormat(fullObject, value, params, property) {
var phonePattern = /^\+?([0-9\- \(\)])*$/;
if (value && value.length && !phonePattern.test(value))
return [ {"policyRequirement": "VALID_PHONE_FORMAT"}];
else
return [];
}
To keep things DRY, my server code gets a handle on each of these functions and calls toString() on them, returning them to the browser as part of a JSON object. Something like this:
{ "name" : "phoneNumber",
"policies" : [
{ "policyFunction" : "\nfunction validPhoneFormat(fullObject, value, params, property) {\n var phonePattern = /^\\+?([0-9\\- \\(\\)])*$/;\n if (value && value.length && !phonePattern.test(value)) {\n return [{\"policyRequirement\":\"VALID_PHONE_FORMAT\"}];\n } else {\n return [];\n }\n}\n"
}
]
}
My browser JS code then takes this response and creates an instance of this function in that context, like so:
eval("var policyFunction = " + this.policies[j].policyFunction);
policyFailures = policyFunction.call(this, form2js(this.input.closest("form")[0]), this.input.val(), params, this.property.name));
This all works very well. However, I then run this code through JSLint, and I get back this message:
[ERROR] ValidatorsManager.js:142:37:eval is evil.
I appreciate that often, eval can be dangerous. However, I have no idea how else I could implement such a mechanism without using it. Is there any way I can do this and also pass through the JSLint validator?
I wouldn't worry about it since you are only passing these function strings from the server to the client, and are thus in control of what will be evaluated.
On the other hand, if you were going the other direction and doing the evals of client-passed code on the server, that would be an entirely different story...
Update:
As disabling the validation option in your comment may cause you to miss future errors, I would instead suggest passing the function name rather than the entire function and have the function library mirrored on the server and client. Thus, to call the function, you'd use the following code:
var policyFunction = YourLibraryName[this.policies[j].policyFunctionName];
var policyArguments = this.policies[j].policyArguments;
policyFunction.apply(this, policyArguments);
Update 2:
I was able to validate the following code with JSLint successfully, which essentially allows you to "turn off" validation for the vast minority of cases where eval is appropriate. At the same time, JSLint still validates normal eval calls, and all uses of this method should throw up flags for future developers to avoid using it/refactor it out where possible/as time allows.
var EVAL_IS_BAD__AVOID_THIS = eval;
EVAL_IS_BAD__AVOID_THIS(<yourString>);
Dont encode a function as a string in JSON. JSON is for content, which you are confounding with behavior.
Instead, I suppose you could return JS files instead, which allow real functions:
{ name : "phoneNumber",
policies : [
{ policyFunction : function() {
whateverYouNeed('here');
}
}
]
}
But while that solves the technical issue, it's still not a great idea.
The real solution here is to move your logic out of your content entirely. Import a JS file full of little validation functions and call them as needed based on a dataType property in your JSON or something. If this functions are as small and portable as you say, this should be trivial to accomplish.
Getting your data all tangled up with your code usually leads to pain. You should statically include your JS, then dynamically request/import/query for your JSON data to run through your statically included code.
I would avoid using eval in all situations. There's no reason you can't code around it. Instead of sending code to the client, just keep it hosted on the server in one contained script file.
If that's not doable, you can also have a dynamically generated javascript file then pass in the necessary parameters via the response, and then dynamically load the script on the client side. There's really no reason to use eval.
Hope that helps.
You can use
setInterval("code to be evaluated", 0);
Internally, if you pass setInterval a string it performs a function similar to eval().
However, I wouldn't worry about it. If you KNOW eval() is evil, and take appropriate precautions, it's not really a problem. Eval is similar to GoTo; you just have to be careful and aware of what you're doing to use them properly.
With very little parsing you could have had it like so:
var body = this.policies[j].policyFunction.substr;
body = body.substr(body.indexOf("(") + 1);
var arglist = body.substr(1, body.indexOf(")"));
body = body.substr(arglist.length + 1);
var policyFunction = new Function(arglist, body);
Which would provide a bit of validation, avoid the literal use of eval and work synchronously with the code. But it is surely eval in disguise, and it is prone to XSS attack. If the malevolent person can get their code loaded and evaluated this way - it will not save you. So, really, just don't do it. Add a <script> tag with the proper URL and that would be certainly safer. Well, you know, better safe then sorry.
PS. My apologises if the code above doesn't work, it only shows the intent, I've not tested it, and if I made a mistake at counting parenthesis or some such - well, you should get the idea, I'm not advertising it by any means.
DRY is definitely something I agree with, however there is a point where copy+pasting is more efficient and easy to maintain than referencing the same piece of code.
The code you're saving yourself from writing seems to be equivalent to a clean interface, and simple boiler plate. If the same code is being used on both the server and the client, you could simply pass around the common pieces of the function, rather than the whole function.
Payload:
{
"name": "phoneNumber",
"type": "regexCheck",
"checkData": "/^\\+?([0-9\\- \\(\\)])*$/"
}
if(payload.type === "regexCheck"){
const result = validPhoneFormat(fullObject, value, payload.checkData)
}
function validPhoneFormat(fullObject, value, regexPattern) {
if (value && value.length && !regexPattern.test(value))
return [ {"policyRequirement": "VALID_PHONE_FORMAT"}];
else
return [];
}
This would give you the ability to update the regex from a single location. If the interface changes it does need to be updated in 2 places, but I wouldn't consider that a bad thing. If the client is running code, why hide the structure?
If you really, really want to keep both the object structure and the patterns in one place - extract it to a single API. Have a "ValidatePhoneViaRegex" api endpoint which is called by all places you'd be passing this serialized function to.
If all of this seems like too much effort, set jslint to ignore your piece of code:
"In JSHint 1.0.0 and above you have the ability to ignore any warning with a special option syntax. The identifier of this warning is W061. This means you can tell JSHint to not issue this warning with the /*jshint -W061 */ directive.
In ESLint the rule that generates this warning is named no-eval. You can disable it by setting it to 0, or enable it by setting it to 1."
https://github.com/jamesallardice/jslint-error-explanations/blob/master/message-articles/eval.md
I would prefer to see copy+pasted code, a common api, or receiving parameters and copy+pasted boiler plate than magical functions passed in from the server to be executed.
What happens if you get a cross-browser compatibility error with one of these shared functions?
Well, the first thing to bear in mind is that jsLint does make the point that "it will hurt your feelings". It's designed to point out where you're not following best practices -- but code that isn't perfect can still work just fine; there's no compulsion upon you to follow jsLint's advice.
Having said that, eval is evil, and in virtually all cases there is always a way around using it.
In this case, you could use a library such as require.js, yepnope.js or some other library that is designed to load a script separately. This would allow you to include the javascript functions you need dynamically but without having to eval() them.
There are probably several other solutions as well, but that was the first one that came to my mind.
Hope that helps.