I am finding that LESS has a hobbled JavaScript evaluator, at least the way I am using it, which is to compile *.less files into *.css on a client before uploading them to the web server.
I'm aware that compilation may be more often done server-side, but for performance & simplicity we only want CSS files on the server. I'm compiling the LESS files on Fedora Linux with the lessc ruby gem installed into Node Package Manager as in these instructions.
The compiler is working perfectly, but as far as I can tell the JavaScript expression evaluation is sorely limited. I believe this also applies to server-side JavaScript expression evaluation based on this posting which suggests uncertainty about how the JavaScript engine is plugged into the LESS environment.
All I can use are simple, comma-separated expressions, like the following:
#bar: `
"ignored-string-expression"
,
5
`;
div.test-thing { content: ~"#{bar}"; }
which compiles into:
div.test-thing {
content: 5;
}
When I try to define a function, the compiler barfs (whether or not the semicolon in the expression is backslash-escaped):
[719] anjaneya% cat testfunc.less
#bar: `function foo() {return 5}; foo()`;
div.test-thing { content: ~"#{bar}"; }
[720] anjaneya% lessc testfunc.less
SyntaxError: JavaScript evaluation error: `function foo() {return 5}; foo()` ...
There also doesn't seem to be any way of looping, even if you try to trick it into evaluating a loop as you would the "ignored-string-expression" above, like:
#foo: `x = 0,
for (var n = 0; n <= 10; n++) { x++; },
x
`;
div.test-thing { content: ~"#{bar}"; }
which says:
ParseError: Syntax Error on line 1 ...
Why bother? To be able to compile this LESS:
#svgSource: '<svg xmlns="http://www.w3.org/2000/svg" width="100%" height="100%"><linearGradient id="g" x1="0" y1="0" x2="0" y2="1"><stop offset="0" stop-color="#{start}" /><stop offset="1" stop-color="#{end}" /></linearGradient><rect x="0" y="0" width="100%" height="100%" fill="url(#g)" /></svg>';
into this CSS:
background: url(data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHdpZHRoPSIxMDAlIiBoZWlnaHQ9IjEwMCUiPjxsaW5lYXJHcmFkaWVudCBpZD0iZyIgeDE9IjAiIHkxPSIwIiB4Mj0iMCIgeTI9IjEiPjxzdG9wIG9mZnNldD0iMCIgc3RvcC1jb2xvcj0iIzU3OWRkYiIgLz48c3RvcCBvZmZzZXQ9IjEiIHN0b3AtY29sb3I9IiMwMDAwMjIiIC8+PC9saW5lYXJHcmFkaWVudD48cmVjdCB4PSIwIiB5PSIwIiB3aWR0aD0iMTAwJSIgaGVpZ2h0PSIxMDAlIiBmaWxsPSJ1cmwoI2cpIiAvPjwvc3ZnPg==);
using a program like this, whether the algorithm is implemented in JavaScript, PHP, Perl, UNIX shell, or anything else. This processing might be done without function definitions but not without looping, and without functions you can't even have recursion.
Given that both functions and looping are compound statements that probably aren't evaluated as expressions (it's not LISP), that is probably the basis for the failure... it's not really a full JavaScript interpreter. So I'm hoping someone who really knows the LESS compiler will:
clarify the limitation above, so I can use JavaScript & LESS portably for this task
say how this problem can be worked around (e.g., with a "shell escape" or any evaluation environment that can process strings iteratively) and/or
say how to extend the LESS compiler with such text processing capabilities, like a "real" JavaScript engine.
The data-uri() function is now built into LESS:
http://lesscss.org/functions/#misc-functions-data-uri
Will that help?
I think what you're looking for is both a mixture of a BUNCH of little frustrating things about using javascript in LESS.
All javascript has to be on one line. (I... don't even.. whatever.)
All javascript has to return something or you get the completely useless error "Cannot read property 'value' of undefined"
All javascript must be one statement. This comes from the original use case where they were thinking you would do something like #foo: ~'something.javascript.is.good.at({#bar});'
Number 1 is formatting, 2 just means you need to return something even if you don't use it, but number 3 catches a lot of people off guard. To get around it, just make you "one thing" a self-executing anonymous function.
Eg:
(function(){
do.some.cool.stuff();
other.cool.things();
return('Fry');
})();
So the LESS parser sees that (make sure it's all in one line instead of how I wrote it!), bundles it off to javascript land as a single execution, reads the return value, and calls it a day.
If you want to see it in action, I recently wrote LESS mixin to make RGBA 1x1 pixels for background fills, etc. that uses all of this madness.
Hope that helps!
I know this post is a couple of years old but javascript embedded in LESS can be very handy so I though I would post some tips:
//All javascript must
// a. be on the rhs of an assignment e.g. #x:` var x = #{val}+7`;
// b. must evaluate to a value
// c. cannot be terminated by a ';'
//
// To get around this, multiline code can be packed into an IIFE......
#val:7;
#loop:`(function(val){
var sum=0;
for(var i=0; i<val; i++){sum+=i;}
return sum;
} )(#{val})`;
.test{
content:#loop; // content: 21;
}
// console.log writes directly to the beginning of the output file
#x:`console.log('/*...... loop = #{loop}.......*/')`; // /*...... loop = 21.......*/
// you can use the global variable. Here we attach a library module to it.....
#x:`global.myLib={}`;
// Then add a method to the module..............
#btoa:`myLib.btoa=function(str){
var buffer = new Buffer((str).toString(), 'binary');
return buffer.toString('base64');
}`;
// And invoke the method to encode some text............................
#sometext:'LESS is more (more or less)';
.test2{
content:`myLib.btoa(#{sometext})`;// content: "TEVTUyBpcyBtb3JlIChtb3JlIG9yIGxlc3Mp";
}
Related
I am trying to puzzle out a way to de-obfuscate javascript that looks like this:
https://jsfiddle.net/douglasg14b/4951br9f/2/
var testString = 'Test | String'
var wf6 = {
fq4: 'su',
k8d: 'bs',
l8z: 'tri',
cy1: 'ng',
t5j: 'te',
ol: 'stS',
x3q: 'tri',
l9x: 'ng',
gh: 'xO'
};
//Obfuscated
let test1 = testString[wf6.fq4 + wf6.k8d + wf6.l8z + wf6.cy1](4,11);
//Normal
let test2 = testString.substring(4,11);
let test3;
//More complex obfuscation
(function moreComplex(){
let h = "i",
w = "nde",
T0 = "f",
hj = '|',
a = eval(wf6.t5j + wf6.ol + wf6.x3q + wf6.l9x).length;
//Obfuscated
test3 = testString[wf6.fq4 + wf6.k8d + wf6.l8z + wf6.cy1](testString[h + w + wf6.gh + T0](hj), a);
//Normal
let test4 = testString.substring(testString.indexOf('|'), testString.length);
})();
$('.span1').text(test1);
$('.span2').text(test3);
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<span class="span1"></span><br>
<span class="span2"></span>
This is a small example, the file I'm working with is ~60k lines long and is full this kind of obfuscation. Everywhere a string can be used as a property name, this kind of obfuscation is used.
The way I can think of doing this, is to evaluate all the string concatenations so they are turned into a readable equivalent. Though, I am not sure how to go about this and ignore all the other working code that exists between all the concatenations.
Thoughts?
Bonus question: Is there a commonly used name for this kind of obfuscation that might make searches a bit easier?
Edit: Added a more complex example.
You have the basic idea right: you have to partially-evaluate the program and precompute all the constant computations. In your case, the constant computations of main interest are the concatenation steps over values which don't change.
To do this, you need a program transformation system (PTS). This is a tool that will read/parse source code for a specified language and build an abstract syntax tree, allow you specify transformations and analyses over the AST, and run those, and then spit out the modified AST as source code again.
In your case, you obviously want a PTS that is wired to know JavaScript out of the box (rare) or is willing to accept a description of JavaScript and then read JavaScript (more typical) with the hope that you can build or get a JavaScript description easily. [I build a PTS that has JavaScript descriptions available, see my bio].
With that in hand, you need to:
code an analyzer that inspects each variable found in an expression to see if that expression is constant (e.g., "wf6"). To demonstrate it is constant, you will have to find the variable definition, and check that all the values used in the variable definition are themselves constants. If there is more than one variable definition, you might have to check that all definitions produce the same value. You need to check for side-effects on the variable (e.g, there are no function calls "foo(...,wf6,...)" which would allow the variable's value to be modified). You need to worry about whether an eval command to accomplish such a side effect exists [this is virtually impossible to do, so you often have to just ignore evals and assume they do not do such things]. Many PTSes will have a way to allow you to build such analyzers; some are easier than others.
For every constant valued variable, substitute the value of that variable in the code
For every constant-valued sub-expression after such substitutions, "fold" (calculate) the result of that expression and substitute that value for that subexpression and repeat until no more folding is possible. Obviously you want to do this for at least all "+" operators. [OP just modified his example; he'll want to do it for "eval" operators too when all its operands are constant].
You may have to iterate this process, as folding an expression may make it obvious that a variable now has a constant value
The above process is called "constant propagation" in the compiler literature and is a feature of many compilers.
In your case, you could restrict the constant folding to just string concatenates. However, once you have adequate machinery to do constant value propagation, doing all or most operators on constants isn't that hard. You may need this to undo other obfuscations involving constants since that
seems to be the obfuscation style used on the code you are working on.
You'll need a special rule that transforms
var['string'](args)
into
var.string(args)
as a final step.
You have another complication: that is knowing that you have all the JavaScript relevant to producing constant-valued variables. A single web page may have many included chunks of JavaScript; you will need all of them to demonstrate there are no side effects on a variable. I assume in your case you are sure you have it all.
With respect to producing known-constant values, you may have worry about a tricky case: an expression that produces constant values from non-constant operands. Imagine the obfuscated expression was:
x=random(); // produce a value between 0 and 1
one=x+(1-x); // not constant by constant propagation, but constant by algebraic relations
teststring['st'[one]+'vu'[one+1]+'bz'[one]+...](4,11)
You can see it always computes 'substring' as a property. You can add a transformation rule that understands the trick used to compute "one", e.g., a rule for each algebraic trick used to compute known constants. Unfortunately for you, there's an infinite number of algebra theorems one can use to manufacture constants; how many are really used in your example bit of code? [Welcome to the problem of reverse engineering with a smart adversary].
Nope, none of this "easy". Presumably that's why the obfuscation method
used was chosen.
Ive got this labratory equipment that is connected to my PC. It uses special OCX file to communicate with the device (reading, setting parameters and such). I got this code from manual that seems to be working. I get a message box saying "Magnification =1272.814 Last error=API not initialized".
<HTML>
<HEAD>
<SCRIPT LANGUAGE="VBScript">
<!--
Sub window_onLoad()
Dim Value
Dim er
call Api1.Initialise("")
call Api1.Get("AP_MAG",Value)
call Api1.GetLastError(er)
call window.alert("Magnification = " + CStr(Value)+"Last error="+er)
call Api1.ClosingControl()
end sub
-->
</SCRIPT>
<TITLE>New Page</TITLE>
</HEAD>
<BODY>
<object classid="CLSID:71BD42C4-EBD3-11D0-AB3A-444553540000" id="Api1">
<PARAM NAME="_Version" VALUE="65536">
<PARAM NAME="_ExtentX" VALUE="2096">
<PARAM NAME="_ExtentY" VALUE="1058">
<PARAM NAME="_StockProps" VALUE="0">
</OBJECT>
</BODY>
</HTML>
So because I have 0% knowledge in vbs and about 10% in jscript I`m trying to rewrite the same thing in Javascript. And I also have some necessary code already written in js.
<script language="JScript">
var Api1=new ActiveXObject("ApiCtrl");
var value;
var er;
Api1.Initialise("");
Api1.Get("AP_MAG",value);
Api1.GetLastError(er);
window.alert("Magnification = " + value+"\n Last error="+er);
Api1.ClosingControl();
</script>
Unfortunately I get a type mismatch error in either .Get or .GetLastError methods either with var value; var er; or var value=""; var er="";
Here is what API manual has to say
long GetLastError(VARIANT* Error)
[out] Error is the error string
associated with the error code for the last error
Remarks: This call will return a VT_BSTR VARIANT associated with the last error. Return
Value: If the call succeeds, it returns 0. If the call fails, an error
code is returned from the function.
long Get(LPCTSTR lpszParam, VARIANT* vValue)
[in] lpszParam is the name of the parameter e.g. “AP_MAG”
[in][out] vValue is the value of the parameter Remarks: This call will get the
value of the parameter specified and return it in vValue. In C++,
before calling this functions you have to specify the variant type
(vValue.vt) to either VT_R4 or VT_BSTR. If no variant type is defined
for vValue, it defaults to VT_R4 for analogue parameters (AP_XXXX) and
VT_BSTR for digital parameters (DP_XXXX). If the variant type is VT_R4
for an analogue parameter, then the floating point representation is
returned in the variant. If a VT_BSTR variant is passed, analogue
values are returned as scaled strings with the units appended (e.g.
AP_WD would return “= 10mm”). For digital parameters, VT_R4 variants
result in a state number and VT_BSTR variants result in a state string
(e.g. DP_RUNUPSTATE would return state 0 or “Shutdown” or the
equivalent in the language being supported). In C++, if the variant
type was specified as VT_BSTR then the API will internally allocate a
BSTR which the caller has to de-allocate using the SDK call
::SysFreeString (vValue.bstrVal)
Welcome to StackOverflow!
Well, each language is made with purpose. Then come to deal with ActiveX objects in browser (or WSH) environment, VBScript is the best choice, while JavaScript is most worst.
JavaScript hasn't so-called out parameters. That mean all function arguments are passed by value (as copy). Lets show you this with examples.
' VBScript
Dim X, Y
X = 1
Y = 2
Foo X, Y
MsgBox "Outer X = " & X & ", Y = " & Y
'> Local args: 6, 8
'> Outer X = 1, Y = 8
Sub Foo(ByVal arg1, ByRef arg2)
arg1 = 6
arg2 = 8
MsgBox "Local args: " & arg1 & ", " & arg2
End Sub
By default in VBS the arguments are passed by reference, so ByRef prefix in function arguments declaration is optional. I include it for clarity.
What the example illustrate is the meaning of "by reference" or "out" parameter. It behave like return value because it modify referenced variable. While modifying "by value" variable has no effect outside of the function scope, because we modify a "copy" of that variable.
// JavaScript
function foo(arg1) {
arg1 = 2;
alert('Local var = ' + arg1);
}
var x = 0;
foo(x);
alert('Outer var = ' + x);
// Local var = 2
// Outer var = 0
Now take a look at this thread. Looks like there is a kind of partial solution by using empty objects. I'm not sure in which cases that will work, but for sure it's very limited hack.
If this not help in your case, then looks like it's time to go with VBScript. Starting with VBS is easy anyway. It's the most user friendly language I ever touch. I was need days, even weeks with other languages only to get started, while just after a few hours with VBS I was able to use it freely.
[EDIT] Well, I made a lot more efforts to reply as may looks like at the glance :) Starting with the language limitation you met. Afterwards going to explain the nature of that limitation (what's "in/out" parameter), and the best way to do that is via example, and this is what I did. Afterwards I show you the only workaround out there to deal with this limitation in JS. Can we consider this as complete answer?
You not mention whether you test this "empty-object-trick", but as you still asking I presume you did that and it's not work with your OCX, right? Then, in this case, you're just forced to deal with your OCX via VBScript, what was my answer from the beginning. And as you prefer to stay with JS then you need to integrate a piece of VB code in your solution.
And as you noted too, this VBs/Js integration is a whole new question. Yes, good question of course, but it's a metter of new topic.
Ok, lets say that the question you append below: "why it should work with passing objects as a function parameter", is still a part of the main question. Well, as you see, even people using JS daily (am not one of them) has no idea what happens "behind the hood", i.e. do not expect an answer on what the JS-engine do in this case, or how this cheat the JS-engine to do something that it's not designed to do. Personally, as I use JS very rarely and not for such tasks, am not even sure if this trick works at all. But as the JS-guys assert it works (in some cases) then we s'd trust them. But that's all about. If this approach fail then it's not an option.
Now what's remain is a bit of homework, you s'd research all available methods for VBs/Js integration, also test them to see which one is most applicable to your domain, and if by chance you meet with difficulties, just then come-back to the forum with new topic and the concrete issue you're trying to resolve.
And to become as helpful as possible, I'll facilitate you with several references to get started.
Here is the plan...
1. If it's possible to work without VBs/Js integration then use stay-alone .VBS files (in WSH environment), else ...
2. In case you work in browser environment (HTML or HTA) then you can embed both (VBs/Js), and your integration w'd be simple.
3. Or may integrate VBs/Js with Windows Script Files (.wsf).
4. Or use ScriptControl that allow running VBScript from within JScript (or backward/opposite).
Links:
Using the ScriptControl
How To Call Functions Using the Script Control
An example VBs/Js integration using ScriptControl via
Batch-Embeded-Script
What is Batch-Embeded-Script:
VBS/Batch Hybrid
JS/Batch Hybrid
5. Some other method (if you find, that am not aware of).
Well, after all this improvements I not see what I can append more, and as I think, now
my answer is more than complete. If you agree with my answer then accept it by clicking on the big white arrow. Of course, if you expect to get better reply from other users, you may still wait, but keep in mind that unanswered questions stay active just for awhile and then become closed.
I am using less.js (1.3.0) to parse less to css on the client side. Inside the parsers' callback I want to get the value for each variable. i tried the following without success.
var data = "#colour: red; #example { background-color: #colour; }",
parser = new less.Parser({});
parser.parse(data, function (error, root) {
console.log( root.toCSS() );
var varsDef = root.variables();
for (k in varsDef) {
console.log(varsDef[k]);
// how to get the value for the var?
//not working
console.log(varsDef[k].eval());
//not working
console.log(varsDef[k].toCSS());
//is an object but looking for a string value
console.log(varsDef[k].value);
//returns an empty string
console.log(varsDef[k].value.toCSS());
}
});
Neither eval() nor the toCSS() gave me any results. I do not understand the less parsers' inner workings. Each variable object has a variable property varsDef[k].value which is an object itself. But I just need the string value of the variable.
Does anyone know how to get the variables' values as a string?
varsDef[k].value.toCSS()
should be the value
varsDef[k].name
should be the variable name
varsDef[k].toCSS()
returns nothing because it is a variable - in CSS variables do not output.
i ran into this problem recently and it bit me because, like you, i had the same instinct of running something like very much like the code you wrote above but for complex variables along the lines of
#redColor: #900; // responds to .toCSS()
#fooColor: desaturate(#redColor, 20%); // both of these error out
#barColor: lighten(#fooColor, 10%); // when calling .toCSS()
you'd get this nested tree.Value for #barColor which was this nested representation of the parse tree, so it would say, unhelpfully that barcolor: {[value: {value: [{lighten: {...}}]}]} or somesuch. my parsing-fu is pretty bad because i would always end up with some object at some point which would no longer respond to me invoking tree.toCSS on it, so i gave up on that route.
Instead, what i did was generated a nonsense .less file with an import rule and a nonsense rule, like so
#import "varfile.less";
.foo {
redColor: #redColor;
fooColor: #fooColor;
barColor: #barColor;
}
less will happily parse such a file, it doesn't care if redColor is a real css property or not, it just ignores it and does all the substitutions where it has to dutifully. And so you actually end up with a single rule css file that you can easily parse since it's very straightforwardly marked up. it looks like this:
.foo{
redColor: #990000;
fooColor: #8a0f0f;
barColor: #b81414;
}
this is, coincidentally, the easiest file to parse. it practically begs to be turned into json or what have you. granted, the path to here is pretty comical. i suspect it's because a variable without a rule is still fair game to be modified within the rule itself, but i could just be rationalizing that.
assuming you only want to extract the final values of your less vars and not the semantic values of your less vars, it's pretty handy. if you want semantics, it seems better to just parse the actual less file.
i ended up writing this in node and after i got past my own objections to how dodgy it felt, it worked quite well and fed me a json dict with my project's variables. you can take a look, it's on github at nsfmc/less-extractor which basically takes a basic config file and then writes to stdout a json dict. it's inelegant, but it totally works, even if it's a bit hackish.
your original question asked about doing this entirely client-side, so that would appear to rule out that github project, but the idea is very similar: you want to be able to access the original less file as part of some xhr request, parse it to get the variable names, build a less string, parse that, and then the rest of the code is just string building and run of the mill parsing.
hope that helps you!
I was also having issues with the less parser too; doing it that way was getting ridiculous with recursive checking of tree nodes.
If you wan't the actual values as opposed to the CSS generated (as per the above answer), the best way is to probably manually parse the file's text.
This function returns a key/value pair for each of the variables in a given less file. It wont work if the LESS file has multiple values per line, you could make it better with regex. I used it to parse bootstrap's variables file, which works nicely.
getLessVars = (lessStr) ->
lines = lessStr.split('\n')
lessVars = {}
for line in lines
if line.indexOf('#') is 0
keyVar = line.split(';')[0].split(':')
lessVars[keyVar[0]] = keyVar[1].trim()
return lessVars
Is there any way to get the source line number in Javascript, like __LINE__ for C or PHP?
There is a way, although more expensive: throw an exception, catch it immediately, and dig out the first entry from its stack trace. See example here on how to parse the trace. The same trick can also be used in plain Java (if the code is compiled with debugging information turned on).
Edit: Apparently not all browsers support this. The good news is (thanks for the comment, Christoph!) that some browsers export source file name and line number directly through the fileName and lineNumber properties of the error object.
The short answer is no.
The long answer is that depending on your browser you might be able to throw & catch an exception and pull out a stack trace.
I suspect you're using this for debugging (I hope so, anyway!) so your best bet would be to use Firebug. This will give you a console object; you can call console.trace() at any point to see what your programme is doing without breaking execution.
You can try to run C preprocessor (f.e. cpp from GNU Compiler Collection) on your javascript files -- either dynamically with each request or statically, by making this operation be applied every time you change your javascript files. I think the javascript syntax is similar enough for this to work.
Then you'd have all the power of C preprocessor.
You can use this in vanilla JS:
function getLine(offset) {
var stack = new Error().stack.split('\n'),
line = stack[(offset || 1) + 1].split(':');
return parseInt(line[line.length - 2], 10);
}
Object.defineProperty(window, '__LINE__', {
get: function () {
return getLine(2);
}
});
You will now have access to the global variable __LINE__
A __LINE__ in C is expanded by a preprocessor which literally replaces it with the line number of the current input. So, when you see
printf("Line Number: %d\r\n", __LINE__);
the compiler sees:
printf("Line Number: %d\r\n", 324);
In effect the number (324 in this case) is HARDCODED into the program. It is only this two-pass mechanism that makes this possible.
I do not know how PHP achieves this (is it preprocessed also?).
I think preprocessing makes more sense, in that it adds no runtime overhead. An alternative to the C preprocessor is using perl, as in the 2 step procedure below:
1 – add “Line # 999 \n” to each line in the script that you want numbered, e.g.,
alert ( "Line # 999 \n"+request.responseText);
2 – run the perl below:
cat my_js.js | perl -ane "{ s/Line # \d+ /Line # $. /; print $_;}" > C_my_js.js; mv C_my_js.js my_js.js
There is one workaround.
Usually the __ LINE __ combined with the __ FILE __ is used for marking a locations in code and the marking is done to find that location later.
However, it is possible to achieve the same effect by using Globally Unique Identifiers (GUID-s) in stead of the __ LINE __ and __ FILE __. Details of the solution reside in the COMMENTS.txt of a BSD-licensed toolset that automates the process.
I know that JavaScript doesn't support macros (Lisp-style ones) but I was wondering if anyone had a solution to maybe simulate macros? I Googled it, and one of the solutions suggested using eval(), but as he said, would be quite costly.
They don't really have to be very fancy. I just want to do simple stuff with them. And it shouldn't make debugging significantly harder :)
You could use parenscript. That'll give you macros for Javascript.
A library by Mozilla (called SweetJS) is designed to simulate macros in JavaScript. For example, you can use SweetJS to replace the function keyword with def.
One can also now use ClojureScript to compile clojure to javascript and get macros that way. Note ClojureScript uses Google Closure.
I've written a gameboy emulator in javascript and I simulate macros for cpu emulation this way:
macro code (the function returns a string with the macro code):
function CPU_CP_A(R,C) { // this function simulates the CP instruction,
return ''+ // sets CPU flags and stores in CCC the number
'FZ=(RA=='+R+');'+ // of cpu cycles needed
'FN=1;'+
'FC=RA<'+R+';'+
'FH=(RA&0x0F)<('+R+'&0x0F);'+
'ICC='+C+';';
}
Using the "macro", so the code is generated "on the fly" and we don't need to make function calls to it or write lots of repeated code for each istruction...
OP[0xB8]=new Function(CPU_CP_A('RB',4)); // CP B
OP[0xB9]=new Function(CPU_CP_A('RC',4)); // CP C
OP[0xBA]=new Function(CPU_CP_A('RD',4)); // CP D
OP[0xBB]=new Function(CPU_CP_A('RE',4)); // CP E
OP[0xBC]=new Function('T1=HL>>8;'+CPU_CP_A('T1',4)); // CP H
OP[0xBD]=new Function('T1=HL&0xFF;'+CPU_CP_A('T1',4)); // CP L
OP[0xBE]=new Function('T1=MEM[HL];'+CPU_CP_A('T1',8)); // CP (HL)
OP[0xBF]=new Function(CPU_CP_A('RA',4)); // CP A
Now we can execute emulated code like this:
OP[MEM[PC]](); // MEM is an array of bytes and PC the program counter
Hope it helps...
function unless(condition,body) {
return 'if(! '+condition.toSource()+'() ) {' + body.toSource()+'(); }';
}
eval(unless( function() {
return false;
}, function() {
alert("OK");
}));
LispyScript is the latest language that compiles to Javascript, that supports macros. It has a Lisp like tree syntax, but also maintains the same Javascript semantics.
Disclaimer: I am the author of LispyScript.
Check out the Linux/Unix/GNU M4 processor. It is a generic and powerful macro processor for any language. It is especially oriented towards Algol-style languages of which JavaScript is a member.
Javascript is interpreted. Eval isn't any more costly that anything else in Javascript.