Support `this` in script functions by NetWin · Pull Request #12 · NetWin/maple

NetWin · 2026-10-20T20:04:53Z

Script functions get JavaScript's strict-mode this. Constructors and prototypes stay unsupported.

What changed

this is the object of a method call, undefined for a plain call and at the top level, and whatever call,
apply and bind pass. Arrows take it from the enclosing function.
Array callbacks, Array.from and the forEach of Map and Set take a thisArg.
A JSON reviver and replacer get the holder as this. A reviver no longer receives the holder as a third argument.
Commit scopes name the area changed instead of the package.

A function that is not an arrow gets strict-mode this: the object of a method call, undefined for a plain call, and the receiver call, apply and bind pass, never boxed. An arrow sees the this of the function it is written in. At the top level this is undefined, since there is no global object. Host functions and intrinsics still receive no this. Constructors and prototypes stay unsupported.

every, filter, find, findIndex, findLast, findLastIndex, flatMap, forEach, map, some, Array.from and the forEach of Map and Set call their callback with the thisArg as this. Every other built-in callback keeps undefined.

A reviver no longer receives the holder as a third argument; it is this instead, as in JavaScript. Use this where a reviver read the third argument.

A function replacer is called with the object holding the key as this, and with a fresh object around the value at the top level, as in JavaScript.

github-actions · 2026-10-20T20:05:20Z

📋 Release Preview

Changelog

0.4.0 (2026-10-20)

🚀 Features

builtins: pass thisArg to array, Map and Set callbacks (80e5ccb)
evaluator: support this in script functions (f90237d)
json: give a JSON replacer its holder as this (d1c1e20)
json: give a JSON reviver its holder as this (7ed2e5f)

📖 Documentation

contributing: update conventional commit instructions (8cc9c43)

Copilot

🔵 Needs a closer look

The broad evaluator, builtin, sandbox, and parity changes warrant final human review.

No open issues 🎉

What changed in this PR

Adds strict-mode this support for Maple script functions, callbacks, and JSON hooks while preserving sandbox isolation.

Changes:

Tracks receivers through scopes, methods, arrows, and function calls.
Adds thisArg support across array, Map, and Set callbacks.
Updates JSON behavior, parity coverage, documentation, and contributor guidance.

File	Summary
`packages/maple/src/evaluator/scope.ts`	Tracks lexical receivers.
`packages/maple/src/evaluator/scope.spec.ts`	Tests receiver scope behavior.
`packages/maple/src/evaluator/functions.spec.ts`	Tests function receiver semantics.
`packages/maple/src/evaluator/evaluator.ts`	Propagates receivers during evaluation and calls.
`packages/maple/src/escapes.spec.ts`	Tests receiver sandbox isolation.
`packages/maple/src/builtins/set/set.spec.ts`	Tests Set callback receivers.
`packages/maple/src/builtins/set/methods/for-each.ts`	Supports Set `thisArg`.
`packages/maple/src/builtins/map/methods/for-each.ts`	Supports Map `thisArg`.
`packages/maple/src/builtins/map/map.spec.ts`	Tests Map callback receivers.
`packages/maple/src/builtins/json/statics/stringify.ts`	Supplies replacer holders as `this`.
`packages/maple/src/builtins/json/statics/parse.ts`	Supplies reviver holders as `this`.
`packages/maple/src/builtins/json/json.spec.ts`	Tests JSON receiver behavior.
`packages/maple/src/builtins/array/utils/array-callback.ts`	Supports callback receiver handling.
`packages/maple/src/builtins/array/statics/from.ts`	Supports `Array.from` `thisArg`.
`packages/maple/src/builtins/array/methods/some.ts`	Passes array callback receivers.
`packages/maple/src/builtins/array/methods/map.ts`	Passes array callback receivers.
`packages/maple/src/builtins/array/methods/for-each.ts`	Passes array callback receivers.
`packages/maple/src/builtins/array/methods/flat-map.ts`	Passes array callback receivers.
`packages/maple/src/builtins/array/methods/find.ts`	Passes array callback receivers.
`packages/maple/src/builtins/array/methods/find-last.ts`	Passes array callback receivers.
`packages/maple/src/builtins/array/methods/find-last-index.ts`	Passes array callback receivers.
`packages/maple/src/builtins/array/methods/find-index.ts`	Passes array callback receivers.
`packages/maple/src/builtins/array/methods/filter.ts`	Passes array callback receivers.
`packages/maple/src/builtins/array/methods/every.ts`	Passes array callback receivers.
`packages/maple/src/builtins/array/array.spec.ts`	Tests array callback receivers.
`packages/maple/docs/security.md`	Documents receiver isolation.
`packages/maple/docs/language.md`	Documents script-function `this`.
`packages/maple/docs/extending.md`	Documents host and intrinsic receiver behavior.
`packages/maple/docs/divergences.md`	Updates documented divergences.
`packages/maple/docs/builtins.md`	Documents callback `thisArg` support.
`packages/maple-parity/src/divergences.spec.ts`	Tests intentional engine divergences.
`packages/maple-parity/src/cases/functions.spec.ts`	Adds parity coverage for `this`.
`packages/maple-parity/README.md`	Updates parity documentation.
`CONTRIBUTING.md`	Updates commit-scope guidance.
`AGENTS.md`	Updates repository conventions.

_{Review effort: Lite}

github-actions · 2026-10-21T19:32:51Z

🎉 This PR is included in version 0.4.0 🎉

The release is available on:

Your semantic-release bot 📦🚀

NetWin added 5 commits October 20, 2026 21:53

feat(builtins): pass thisArg to array, Map and Set callbacks

80e5ccb

every, filter, find, findIndex, findLast, findLastIndex, flatMap, forEach, map, some, Array.from and the forEach of Map and Set call their callback with the thisArg as this. Every other built-in callback keeps undefined.

feat(json): give a JSON reviver its holder as this

7ed2e5f

A reviver no longer receives the holder as a third argument; it is this instead, as in JavaScript. Use this where a reviver read the third argument.

feat(json): give a JSON replacer its holder as this

d1c1e20

A function replacer is called with the object holding the key as this, and with a fresh object around the value at the top level, as in JavaScript.

docs(contributing): update conventional commit instructions

8cc9c43

Copilot AI lite review requested due to automatic review settings October 20, 2026 20:04

Copilot started reviewing on behalf of NetWin October 20, 2026 20:05

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Copilot AI reviewed Oct 20, 2026

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NetWin marked this pull request as ready for review October 20, 2026 20:12

NetWin merged commit 0804400 into increment Oct 20, 2026
8 checks passed

NetWin deleted the feat/this branch October 20, 2026 20:13

NetWin mentioned this pull request Oct 21, 2026

Release: 0.4.0 🚀 #14

Merged

github-actions Bot added the released label Oct 21, 2026

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Support `this` in script functions - #12

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NetWin commented Oct 20, 2026

What changed

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github-actions Bot commented Oct 20, 2026

📋 Release Preview

Changelog

0.4.0 (2026-10-20)

🚀 Features

📖 Documentation

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