Kiesel Devlog #3: Accessors, Date/Map/Set, test262 history graph

Published on 2023-09-26.

Accessors in Object Expressions

I first implemented the fairly similar object method definition syntax ({ foo() {} }), but cheated with the AST representation — this would output the same structure as { foo: function() {} }, which obviously falls apart when the definition has a get or set prefix.

One small refactor later I had an object_define_method bytecode instruction tailored to this use case, which then allowed me to implement getters and setters easily by passing a method, get, or set enum argument to the instruction. The underlying accessor property mechanism was already working and used for some builtin objects.

Demo of accessor properties in the Kiesel REPL

The generated bytecode looks like this (the indices refer to the constant and function expression tables embedded in the executable):

> { foo() {}, get bar() {}, set baz(arg) {} }
Generated Bytecode
------------------
 0: object_create
 1: load
 2: store_constant "foo" [0]
 5: load
 6: object_define_method [0] (type: method)
11: load
12: store_constant "bar" [1]
15: load
16: object_define_method [1] (type: get)
21: load
22: store_constant "baz" [2]
25: load
26: object_define_method [2] (type: set)
31: <end>

{ "foo": fn foo, "bar": <accessor>, "baz": <accessor> }
>

Or, in the case of a computed property (that store_constant + load sequence can be optimized to a single load_constant instruction eventually):

> { get [foo + "bar"]() {} }
Generated Bytecode
------------------
 0: object_create
 1: load
 2: resolve_binding foo [0] (strict: false)
 7: get_value
 8: load
 9: store_constant "bar" [0]
12: load
13: apply_string_or_numeric_binary_operator (operator: +)
16: load
17: object_define_method [0] (type: get)
22: <end>

New Builtins!

TL;DR:

Finished implementing Array.prototype
Added most of Date including basic parsing, no non-UTC time zones yet
Added all of Map and Set, including their iterators

This amounts to a almost 100 new functions!

Demo of the Date object in the Kiesel REPL Demo of the Set object in the Kiesel REPL Demo of date string parsing in the Kiesel REPL Demo of the Map object in the Kiesel REPL

A lot of this was fairly repetitive (Date having a getter and setter for both local time and UTC, as well as Map and Set being nearly identical), but it was still fun to implement these :^)

Expand to see the full list of newly implemented builtins 📝

Array.prototype.concat()
Array.prototype.copyWithin()
Array.prototype.fill()
Array.prototype.flat()
Array.prototype.flatMap()
Array.prototype.reduce()
Array.prototype.reduceRight()
Array.prototype.reverse()
Array.prototype.slice()
Array.prototype.sort()
Array.prototype.splice()
Array.prototype.toReversed()
Array.prototype.toSorted()
Array.prototype.toSpliced()
Date()
Date.now()
Date.parse()
Date.prototype.getDate()
Date.prototype.getDay()
Date.prototype.getFullYear()
Date.prototype.getHours()
Date.prototype.getMilliseconds()
Date.prototype.getMinutes()
Date.prototype.getMonth()
Date.prototype.getSeconds()
Date.prototype.getTime()
Date.prototype.getTimezoneOffset()
Date.prototype.getUTCDate()
Date.prototype.getUTCDay()
Date.prototype.getUTCFullYear()
Date.prototype.getUTCHours()
Date.prototype.getUTCMilliseconds()
Date.prototype.getUTCMinutes()
Date.prototype.getUTCMonth()
Date.prototype.getUTCSeconds()
Date.prototype.setDate()
Date.prototype.setFullYear()
Date.prototype.setHours()
Date.prototype.setMilliseconds()
Date.prototype.setMinutes()
Date.prototype.setMonth()
Date.prototype.setSeconds()
Date.prototype.setTime()
Date.prototype.setUTCDate()
Date.prototype.setUTCFullYear()
Date.prototype.setUTCHours()
Date.prototype.setUTCMilliseconds()
Date.prototype.setUTCMinutes()
Date.prototype.setUTCMonth()
Date.prototype.setUTCSeconds()
Date.prototype.toDateString()
Date.prototype.toISOString()
Date.prototype.toJSON()
Date.prototype.toLocaleDateString()
Date.prototype.toLocaleString()
Date.prototype.toLocaleTimeString()
Date.prototype.toString()
Date.prototype.toTimeString()
Date.prototype.toUTCString()
Date.prototype.valueOf()
Date.prototype[@@toPrimitive]()
Date.UTC()
Map()
Map.prototype.clear()
Map.prototype.delete()
Map.prototype.entries()
Map.prototype.forEach()
Map.prototype.get()
Map.prototype.has()
Map.prototype.keys()
Map.prototype.set()
Map.prototype.size
Map.prototype.values()
Map.prototype[@@iterator]()
Map.prototype[@@toStringTag]
Math.max()
Math.min()
Set()
Set.prototype.add()
Set.prototype.clear()
Set.prototype.delete()
Set.prototype.entries()
Set.prototype.forEach()
Set.prototype.has()
Set.prototype.keys()
Set.prototype.size
Set.prototype.values()
Set.prototype[@@iterator]()
Set.prototype[@@toStringTag]
String.prototype.concat()
String.prototype.repeat()
String.prototype.slice()

A History Graph for test262.fyi

As mentioned in the previous devlog, test262.fyi was updated to start collecting historic data instead of only keeping results for the last run. The obvious use case is a graph comparing all engines against the total number of tests, which I've implemented using Chart.js:

Screenshot of the test262.fyi website showing a history graph for Kiesel

This isn't on the live site yet, but I hope to upstream it soon. You can also see that Kiesel passed the 30% mark two days ago! :^)

What's Next?

Promises or typed arrays probably, both of which are relatively large and will probably have an entire devlog dedicated to them, which is why I'm writing this one now to have a clean slate.

Ignoring async/await promises aren't used that much within ECMAScript itself, but typed arrays bring a whole lot of related functionality with them (ArrayBuffer/SharedArrayBuffer, DataView, Atomics).

Also check out these posts from friends across the web!

Messenger Rooms Bug Bounty Write-up
2020-04-24 — Jane Manchun Wong’s Personal Blog
Bringing SerenityOS to real hardware, one driver at a time
2025-01-08 — sdomi's weblog
Time to break some habits
2024-11-05 — lnl's weblog
Porffor's January 2025 Goals
2025-01-06 — goose.icu