Compile (a subset of) JavaScript or AS2 to ActionScript 2 (Flash Player 8 compatible) bytecode assembly compilable by Flasm. Extremely WIP.
I'm modding an old Flash game and I got tired of writing ActionScript bytecode by hand. Luckily, ActionScript 2 is extremely similar to JavaScript (since AS2 partially conforms to the ECMAScript 4 spec) so I can just use @babel/parser to parse my source as JavaScript into an AST, and then emit the bytecode from the AST.
The compiler only supports a subset of JS/AS2 features I need, and the project reserves the right to butcher semantics of the language to make it easier to implement. Development will also progress only when I find features I want to implement to make my life easier.
The compiler also simulates the stack to document the current stack as comments to the right of each line to make manual verification easier. If a branch or branchIfTrue opcode is reached (an if-else or a loop), the simulator skips rest of the function/context. Inner functions are simulated with their own stacks. Code statements are also added as comments before the bytecode for said statement.
Current work-in-progress sample source:
outsideGlobalVar = globalVar2 = 123;
function gatherStats(velocity) {
var emptyLocal, emptyLocal2, nonEmptyLocal3;
var localVar = 123;
globalVar = 5432;
globalVar = localVar = 1111;
globalVar = globalVar2 = 1111;
globalVar = globalVar2 = undefined;
velocity = atv.velocity;
globalVelocity = atv.velocity;
atv.bar = 1;
this.foo = this.bar + 1;
atv.x = atv.velocityX - atv.x;
localVar = "foo\\nbar";
return '{"type":"velocity","data":' + (velocity + 1) + "}";
}
global.enqueueStats(gatherStats(atvMC.velocity), 1);
enqueueStats(gatherStats(atvMC.velocity));
emptyFunction();
global.emptyFunction();Emits:
//-- outsideGlobalVar = globalVar2 = 123;
//-- outsideGlobalVar = globalVar2 = 123
push 'outsideGlobalVar' // 'outsideGlobalVar'
//-- globalVar2 = 123
push 'globalVar2', 123 // 'outsideGlobalVar' | 'globalVar2' | 123
setVariable // 'outsideGlobalVar'
push 123 // 'outsideGlobalVar' | 123
setVariable // --<empty>
function2 'gatherStats' (r:2='velocity') (r:1='this')
//-- var emptyLocal, emptyLocal2, nonEmptyLocal3;
//-- var localVar = 123;
push 123 // 123
setRegister r:6 /*local:localVar*/ // 123
pop // --<empty>
//-- globalVar = 5432;
//-- globalVar = 5432
push 'globalVar', 5432 // 'globalVar' | 5432
setVariable // --<empty>
//-- globalVar = localVar = 1111;
//-- globalVar = localVar = 1111
push 'globalVar' // 'globalVar'
//-- localVar = 1111
push 1111 // 'globalVar' | 1111
setRegister r:6 /*local:localVar*/ // 'globalVar' | 1111
setVariable // --<empty>
//-- globalVar = globalVar2 = 1111;
//-- globalVar = globalVar2 = 1111
push 'globalVar' // 'globalVar'
//-- globalVar2 = 1111
push 'globalVar2', 1111 // 'globalVar' | 'globalVar2' | 1111
setVariable // 'globalVar'
push 1111 // 'globalVar' | 1111
setVariable // --<empty>
//-- globalVar = globalVar2 = undefined;
//-- globalVar = globalVar2 = undefined
push 'globalVar' // 'globalVar'
//-- globalVar2 = undefined
push 'globalVar2', UNDEF // 'globalVar' | 'globalVar2' | UNDEF
setVariable // 'globalVar'
push UNDEF // 'globalVar' | UNDEF
setVariable // --<empty>
//-- velocity = atv.velocity;
//-- velocity = atv.velocity
push 'atv' // 'atv'
getVariable // atv
push 'velocity' // atv | 'velocity'
getMember // atv.velocity
setRegister r:velocity // atv.velocity
pop // --<empty>
//-- globalVelocity = atv.velocity;
//-- globalVelocity = atv.velocity
push 'globalVelocity', 'atv' // 'globalVelocity' | 'atv'
getVariable // 'globalVelocity' | atv
push 'velocity' // 'globalVelocity' | atv | 'velocity'
getMember // 'globalVelocity' | atv.velocity
setVariable // --<empty>
//-- atv.bar = 1;
//-- atv.bar = 1
push 'atv' // 'atv'
getVariable // atv
push 'bar', 1 // atv | 'bar' | 1
setMember // --<empty>
//-- this.foo = this.bar + 1;
//-- this.foo = this.bar + 1
push r:this, 'foo', r:this, 'bar' // r:this | 'foo' | r:this | 'bar'
getMember // r:this | 'foo' | r:this.bar
push 1 // r:this | 'foo' | r:this.bar | 1
add // r:this | 'foo' | r:this.bar+1
setMember // --<empty>
//-- atv.x = atv.velocityX - atv.x;
//-- atv.x = atv.velocityX - atv.x
push 'atv' // 'atv'
getVariable // atv
push 'x', 'atv' // atv | 'x' | 'atv'
getVariable // atv | 'x' | atv
push 'velocityX' // atv | 'x' | atv | 'velocityX'
getMember // atv | 'x' | atv.velocityX
push 'atv' // atv | 'x' | atv.velocityX | 'atv'
getVariable // atv | 'x' | atv.velocityX | atv
push 'x' // atv | 'x' | atv.velocityX | atv | 'x'
getMember // atv | 'x' | atv.velocityX | atv.x
subtract // atv | 'x' | atv.velocityX-atv.x
setMember // --<empty>
//-- localVar = "foo\\nbar";
//-- localVar = "foo\\nbar"
push 'foo\nbar' // 'foo\nbar'
setRegister r:6 /*local:localVar*/ // 'foo\nbar'
pop // --<empty>
//-- return '{"type":"velocity","data":' + (velocity + 1) + "}";
push '{"type":"velocity","data":', r:velocity, 1 // '{"type":"velocity","data":' | r:velocity | 1
add // '{"type":"velocity","data":' | r:velocity+1
add // '{"type":"velocity","data":'+(r:velocity+1)
push '}' // '{"type":"velocity","data":'+(r:velocity+1) | '}'
add // ('{"type":"velocity","data":'+(r:velocity+1))+'}'
return // ('{"type":"velocity","data":'+(r:velocity+1))+'}'
end // of function gatherStats
//-- global.enqueueStats(gatherStats(atvMC.velocity), 1);
push 1, 'atvMC' // 1 | 'atvMC'
getVariable // 1 | atvMC
push 'velocity' // 1 | atvMC | 'velocity'
getMember // 1 | atvMC.velocity
push 1, 'gatherStats' // 1 | atvMC.velocity | 1 | 'gatherStats'
callFunction // 1 | gatherStats(atvMC.velocity)
push 2, 'global' // 1 | gatherStats(atvMC.velocity) | 2 | 'global'
getVariable // 1 | gatherStats(atvMC.velocity) | 2 | global
push 'enqueueStats' // 1 | gatherStats(atvMC.velocity) | 2 | global | 'enqueueStats'
callMethod // global.enqueueStats(gatherStats(atvMC.velocity), 1)
pop // --<empty>
//-- enqueueStats(gatherStats(atvMC.velocity));
push 'atvMC' // 'atvMC'
getVariable // atvMC
push 'velocity' // atvMC | 'velocity'
getMember // atvMC.velocity
push 1, 'gatherStats' // atvMC.velocity | 1 | 'gatherStats'
callFunction // gatherStats(atvMC.velocity)
push 1, 'enqueueStats' // gatherStats(atvMC.velocity) | 1 | 'enqueueStats'
callFunction // enqueueStats(gatherStats(atvMC.velocity))
pop // --<empty>
//-- emptyFunction();
push 0, 'emptyFunction' // 0 | 'emptyFunction'
callFunction // emptyFunction()
pop // --<empty>
//-- global.emptyFunction();
push 0, 'global' // 0 | 'global'
getVariable // 0 | global
push 'emptyFunction' // 0 | global | 'emptyFunction'
callMethod // global.emptyFunction()
pop // --<empty>Clone the repo, and run npm i. Then, run npm start, or install it as a local relative npm module and run it as js-to-flasm-as2-compiler inside package.json
js-to-flasm-as2-compiler [configFilePath]
$ npm start
> [email protected] start D:\Projects\js-to-flasm-compiler
> node ./bin/index.js
samples\A.js -> dist\A.flm
samples\B.js -> dist\B.flm
empty file samples\Ca.js
samples\Caa.js -> dist\Caa.flm
samples\hooks\foobar\initialize-socket-hook.js -> dist\hooks\foobar\initialize-socket-hook.flmIf you're on Linux, you can probably just
chmod u+x bin/index.js
ln -s $PWD/bin/index.js ./js-to-flasm-as2-compiler
./js-to-flasm-as2-compilerThe compiler will compile the JS source files in samples/, and emit output to the dist/ directory.
The compiler crashes if you use JS features that I haven't implemented.
The comments are also //-- and /*--[[ --]]*/ because Flasm's comments are // and /* */, but I use Lua's syntax highlighting for FLM (it's good enough!) and Lua's are -- and --[[ --]].
- Only
varis supported (noletorconst)- Variables are scoped to the current function, or to the global scope
ifdoesn't support logical binary operators- Logical expressions are not implemented (no
&&or||), though!is
- Logical expressions are not implemented (no
classis not implemented, use prototype based programming (make a function that is a constructor and assign functions to Ctor.prototype)- a lot of features are not implemented
- feature list: see what compiles
- Use
int()instead ofparseInt()- so instead of
var foo = parseInt(bar)dovar foo = int(bar) - int's and parseInt's semantics probably differ, I don't know
- compiles into the
intopcode
- so instead of
- Computed properties only support side-effect free expressions
foo[bar]orfoo['bar']orfoo[x + y + 1 + true + 0]is okay, butfoo[bar++]orfoo[selector()]will fail to compile- I tried to implement it but it was nontrivial to implement
- sorry
- Prefix increment/decrement operator is only implemented for variables, not member expressions
- so
++variableworks but++foo.baror++foo[bar]does not - no real blocker here, just haven't needed it and thus haven't taken the time to implement
- so
- Postfix increment/decrement operator not implemented
variable++orvariable++is not implemented- It's hard to implement with my current compiler design
- Give me a break, it's the first compiler I've written
The compiler searches for a config file named js-to-flasm.config.json in the current directory, or from a path specified by the first argument passed to it.
E.g.
js-to-flasm-as2-compiler ./config/js-to-flasm.config.json
Example config file:
{
"dist": "dist/",
"sourceRoot": "samples/"
}No other keys are supported, and both are required. Both file paths can be anything that node's fs.readdir() understands. Terminating / is probably optional.
Compiler directives are implemented via single-line comments. Directives are not searched for inside block comments or JSDoc comments. A directive is of form:
// directive-name
or if it accepts arguments, it is of form:
// directive-with-args: arg1 arg2 arg3 argn
Current directives are:
Allows you to tell the compiler about register<->variable associations. For example, if you're compiling code that gets #include'd inside a function that you don't control (i.e. it's disassembled code), and you want to access this inside the function, you can instruct the compiler that it's in register n.
Pop the context once you don't need it anymore.
Example 1
// @js2f/push-register-context: r:1=this
enqueueSocketJob('{"type": "cash", "data":' + this.cash + "}");
// @js2f/pop-register-contextExample 2
// @js2f/push-register-context: r:3=socket
socket.onConnect = function () {
// can use local variables here
var foobar = 123;
};
// @js2f/pop-register-contextMIT, see LICENSE.