Dirk
LightNews LightNews
ddv.tools
Dirk
@ddv.tools
14 followers 110 following 21 posts
Backends & tooling. Working on a JS runtime, Maligator, for learning purposes.
GH: @dirkdev98
Posts Replies Media Videos
ddv.tools
Also started to work on static-semantics. With this we should get a good idea of variable scopes, if they are captured by closures and more, so we can hand over this information to the engine.

For now, we collect the different scopes and the initialization of variables and parameters.
February 16, 2026 at 7:02 AM
ddv.tools
With support for for-loops, `new String()` and various new prototype methods, our Test262 number just went up to 4166.
February 16, 2026 at 7:02 AM
ddv.tools
And finally, a Test262 runner! We skip like ~40% of the tests and only pass ~5%. But the number goes up, so that's great!
Screenshot showing my Test262 runner: Output: ``` [TEST262 +260ms] Using 52882 cached files. [TEST262 +1037ms] Progress: 3000 / 52882 [TEST262 +405ms] Progress: 6000 / 52882 [TEST262 +461ms] Progress: 9000 / 52882 [TEST262 +359ms] Progress: 12000 / 52882 [TEST262 +862ms] Progress: 15000 / 52882 [TEST262 +637ms] Progress: 18000 / 52882 [TEST262 +458ms] Progress: 21000 / 52882 [TEST262 +401ms] Progress: 24000 / 52882 [TEST262 +229ms] Progress: 27000 / 52882 [TEST262 +448ms] Progress: 30000 / 52882 [TEST262 +347ms] Progress: 33000 / 52882 [TEST262 +47ms] Progress: 36000 / 52882 [TEST262 +736ms] Progress: 39000 / 52882 [TEST262 +798ms] Progress: 42000 / 52882 [TEST262 +926ms] Progress: 45000 / 52882 [TEST262 +763ms] Progress: 48000 / 52882 [TEST262 +1373ms] Progress: 51000 / 52882 [TEST262 +195ms] Result: { FAILED: 29878, SKIPPED: 19777, PASSED: 2933, STRICT_FAILED: 294 } [TEST262 +1ms] { "uniqueFailureReasons": 2055, "failures": [ { "reason": "No evaluator for node type: ClassDeclaration", "count": 3200, "paths": [ "test/language/statements/class/gen-method/forbidden-ext/b2/cls-decl-gen-meth-forbidden-ext-indirect-access-prop-caller.js", <snip> ```
February 8, 2026 at 9:37 PM
ddv.tools
And the combination of try-catch, Array#map and Function#bind brings the following.

With a TIL: Array#map works on many object-likes that have the `{ length }` property. Note that the callback is only called here if the element of an index exists as well. Otherwise, use `Array.from({ length })`.
Example showing various Maligator features: ``` 1 │ try { 2 │ Array.prototype.map.call({ length: Math.pow(2, 32)}, function() {}) 3 │ } catch (e) { 4 │ e.message; 5 │ } ``` Outputs: EngineValue { type: 'string', data: { value: 'Array length must be a finite integer <= 2^32 - 1.' } }
February 8, 2026 at 9:37 PM
ddv.tools
The switch-implementation is not fully complete yet. We don't evaluate any `case` blocks after the default-case yet.

Making this post revealed a bug in CompletionRecord-handling. The `break;` value is returned from the script instead of the final statement. Got that fixed now as well.
Showcase of switch-statement and array- and object-literals. ``` 1 │ const x = [1,2,3]; 2 │ const y = { x }; 3 │ 4 │ switch (y.x[0]) { 5 │ case 1: 6 │ y.hit = true; 7 │ break; 8 │ default: 9 │ y.hit = false; 10 │ } 11 │ 12 │ y.hit; ``` EngineValue { type: 'boolean', data: { value: true } }
February 8, 2026 at 9:37 PM
ddv.tools
Some more has gone in to Maligator, my JS runtime implemented in TypeScript.
I've started with the real basic intrinsics and finally a way to create JS objects. Combine that with member expressions and we have `[object Object]`.
Local.js code snippet ``` // function fibonacciRecursive(n) { // if (n < 2) { // return n; // } // return fibonacciRecursive(n - 1) + fibonacciRecursive(n - 2); // } // // fibonacciRecursive(11); let x = Object(null); x.foo = Object(null); x.foo.toString(); ``` Result from running that via Maligator `EngineValue { type: 'string', data: { value: '[object Object]' } }`
January 18, 2026 at 2:19 PM
ddv.tools
And with a final push of adding TODO's everywhere, we got function declarations and calling working 🤓
Execution of local.js via Maligator: ``` function add(a, b) { return a + b; } add(1, 2); ``` With result: ``` EngineValue { type: 'number', data: { value: 3 } } ```
January 12, 2026 at 9:21 PM
ddv.tools
Builtin function calls landed in Maligator! Now supporting calling isFinite, isNaN, parseInt and parseFloat :)
Code snippet containing JS: const int = parseInt("5", 10) const finite = isFinite(int); finite; Shell executing Maligator: maligator [main][+241/-][ v24.12.0] ❯ node ./src/engine/tmp.ts { type: 'normal', value: EngineValue { type: 'boolean', data: { value: true } } }
January 11, 2026 at 7:03 PM
ddv.tools
With if-statements and (do-)while-loops supported in Maligator, it all starts to get some shape.
let x = 0; while (true) { if (x === 2) { break; } x++; } x; ❯ node ./src/engine/tmp.ts { type: 'normal', value: EngineValue { type: 'number', data: { value: 2 } } }
January 10, 2026 at 8:39 AM
ddv.tools
Chipped away at a few more things, so updating variables is supported as well. As well as some relational expressions. Next up are the if-, while-, etc-statements.
❯ node ./src/engine/tmp.ts 'let x = 1, y = 2; let xSmallerThenOne = 1 < 2; x++; x === y && xSmallerThenOne' { type: 'normal', value: EngineValue { type: 'boolean', data: { value: true } } }
January 8, 2026 at 7:19 AM
ddv.tools
Got basic variables going! Skipped the static semantics for now, which suggest to initialize all new variable bindings before executing a block.
Also an interesting thing in the spec is that `undefined` and a few others are properties on `global`. So only now can `undefined` actually be resolved.
❯ node ./src/engine/tmp.ts 'let x = 5, y = 5; { x + y; }' { type: 'normal', value: EngineValue { type: 'number', data: { value: 10 } } }
January 5, 2026 at 7:16 PM
ddv.tools
Figured it was time to get code running, so dove straight in to environment records, realms and execution context. For parsing, we just use Meriyah for now.
So with all that prep work, implementing binary expressions (1 + "foo") was really straight-forward.
Screenshot of terminal showing various executions of simple JS additions via the custom JS engine using 'node ./scr/engine/tmp.ts' [arg]'. Where arg is '"foo" + "bar"' or 'true + 1'
January 5, 2026 at 7:04 AM