import { describe, expect, test } from "bun:test" import { Effect } from "effect" import { CodeMode } from "../src/index.js" import { ToolRuntime } from "../src/tool-runtime.js" // Runs a CodeMode program with no host tools and returns the CodeMode.Result. These tests pin the // JS-parity behaviors for the "99% of ordinary defensive JavaScript just works" goal: cases where // a strict interpreter would throw but idiomatic JS yields undefined / succeeds. // // Note on the result boundary: this package normalizes a bare `undefined` result to `null` when // it crosses out of CodeMode (results are JSON data), so tests asserting an in-CodeMode // `undefined` read check `=== undefined` inside the program and `null` at the boundary. const run = (code: string) => Effect.runPromise(CodeMode.execute({ code, tools: {} })) const value = async (code: string) => { const result = await run(code) if (!result.ok) throw new Error(`expected success, got ${result.error.kind}: ${result.error.message}`) return result.value } const error = async (code: string) => { const result = await run(code) if (result.ok) throw new Error(`expected failure, got value ${JSON.stringify(result.value)}`) return result.error } describe("H2: string property access reads as undefined (not a throw)", () => { test("unknown property on a string is undefined", async () => { expect(await value(`const s = "hi"; return s.login === undefined`)).toBe(true) expect(await value(`const s = "hi"; return s.login`)).toBeNull() }) test("optional chaining + fallback on a string does not throw", async () => { expect(await value(`const s = "hi"; return s?.login ?? "fallback"`)).toBe("fallback") }) test("the real MCP pattern: result is a JSON string, defensive read falls through", async () => { // me.result is a string; me.result?.login is undefined, so we fall back to the raw string. expect(await value(`const me = { result: '{"login":"x"}' }; return me.result?.login ?? me.result`)).toBe( '{"login":"x"}', ) }) test("unknown property on a number is undefined", async () => { expect(await value(`return (5).foo ?? "n"`)).toBe("n") }) test("only canonical string index keys access characters", async () => { expect( await value(` const text = "abc" return [text[1], text["1"], text["01"], text["1.0"], text[-0], text["-0"]] `), ).toEqual(["b", "b", null, null, "a", null]) }) }) describe("H3: array property access reads as undefined (not a throw)", () => { test("unknown property on an array is undefined", async () => { expect(await value(`return [1,2,3].foo === undefined`)).toBe(true) expect(await value(`return [1,2,3].foo`)).toBeNull() }) test("optional chaining on an array does not throw", async () => { expect(await value(`return [1,2,3]?.foo ?? "fb"`)).toBe("fb") }) test("unknown property reads stay undefined for methods CodeMode does not implement", async () => { expect(await value(`return [1,2,3].unknownMethod === undefined`)).toBe(true) }) test("array indexing still works", async () => { expect(await value(`return [1,2,3][9] === undefined`)).toBe(true) expect(await value(`return [1,2,3][9]`)).toBeNull() }) test("only canonical array index keys access elements", async () => { expect( await value(` const values = ["a", "b"] return [values[1], values["1"], values["01"], values["1.0"], values[-0], values["-0"]] `), ).toEqual(["b", "b", null, null, "a", null]) }) test("noncanonical keys cannot mutate or delete an aliased element", async () => { expect( await value(` const values = ["a", "b"] let writes = 0 try { values["01"] = ++writes } catch {} const removed = delete values["01"] return [writes, removed, values] `), ).toEqual([0, true, ["a", "b"]]) }) test("the maximum array length is not accepted as an array index", async () => { expect( await value(` const values = [] let writes = 0 try { values["4294967295"] = ++writes } catch {} return [writes, values.length] `), ).toEqual([0, 0]) }) }) describe("H6: object spread of null/undefined is a no-op", () => { test("spreading null is a no-op", async () => { expect(await value(`const o = null; return { ...o, a: 1 }`)).toEqual({ a: 1 }) }) test("spreading an absent argument merges cleanly", async () => { expect(await value(`function f(opts){ return { ...opts, a: 1 } } return f(undefined)`)).toEqual({ a: 1 }) }) test("spreading a real object still works", async () => { expect(await value(`const o = { a: 1 }; return { ...o, b: 2 }`)).toEqual({ a: 1, b: 2 }) }) test("spreading an array into an object still errors", async () => { const err = await error(`return { ...[1,2], a: 1 }`) expect(err.kind).toBe("InvalidDataValue") }) }) describe("H4: typeof on an undeclared identifier is 'undefined'", () => { test("feature-detection guard does not throw", async () => { expect(await value(`return typeof foo === "undefined" ? "safe" : "no"`)).toBe("safe") }) test("typeof of a declared binding is unaffected", async () => { expect(await value(`const x = 5; return typeof x`)).toBe("number") expect(await value(`const s = "a"; return typeof s`)).toBe("string") }) test("referencing an undeclared identifier outside typeof still throws", async () => { const err = await error(`return foo + 1`) expect(err.message).toContain("foo") }) }) describe("CodeMode lexical scope integration", () => { test("keeps self, cross, and destructuring defaults in the TDZ", async () => { expect( await value(` const outer = 1 const errors = [] try { const first = second, second = 2 } catch (error) { errors.push(error.name) } try { const [first = second, second = 2] = [] } catch (error) { errors.push(error.name) } return errors `), ).toEqual(["ReferenceError", "ReferenceError"]) }) test("keeps typeof and constant assignment inside the TDZ", async () => { expect( await value(` const errors = [] try { { errors.push(typeof item); let item } } catch (error) { errors.push(error.name) } try { { constant = 1; const constant = 2 } } catch (error) { errors.push(error.name) } return errors `), ).toEqual(["ReferenceError", "ReferenceError"]) }) test("shadows builtins from the start of the program scope", async () => { expect( await value(` let observed try { observed = typeof Promise } catch (error) { observed = error.name } const Promise = 1 return observed `), ).toBe("ReferenceError") }) test("keeps classic for initializers inside the header TDZ", async () => { expect( await value(` let index = 1 try { for (let index = index; index < 2; index++) {} } catch (error) { return error.name } `), ).toBe("ReferenceError") }) test("removes loop scopes when per-iteration initialization fails", async () => { expect( await value(` const value = "outer" try { for (let [value] of [1]) {} } catch {} return value `), ).toBe("outer") }) }) describe("unary void", () => { test("evaluates its operand and returns undefined", async () => { expect( await value(`let count = 0; const result = void (count += 1); return [count, result === undefined]`), ).toEqual([1, true]) }) test("discards opaque values", async () => { expect(await value(`return void tools === undefined`)).toBe(true) }) }) describe("property deletion", () => { test("deletes plain object fields and reports missing fields as successful", async () => { expect( await value(` const object = { keep: 1, remove: 2 } return [delete object.remove, delete object.missing, object] `), ).toEqual([true, true, { keep: 1 }]) }) test("evaluates computed object and key expressions once", async () => { expect( await value(` const object = { remove: true } let objectReads = 0 let keyReads = 0 function getObject() { objectReads++; return object } function getKey() { keyReads++; return "remove" } const removed = delete getObject()[getKey()] return [removed, objectReads, keyReads, Object.hasOwn(object, "remove")] `), ).toEqual([true, 1, 1, false]) }) test("deleting an array index creates a hole without changing its length", async () => { expect( await value( `const values = [1, 2, 3]; const removed = delete values[1]; return [removed, values.length, 1 in values, values]`, ), ).toEqual([true, 3, false, [1, null, 3]]) }) test("array length is not configurable", async () => { expect(await value(`const values = [1, 2]; return [delete values.length, values.length]`)).toEqual([false, 2]) }) test("does not broaden unsupported array property assignment", async () => { expect( await value(` const values = [] let rightHandSideRuns = 0 function next() { rightHandSideRuns++; return 1 } try { values.field = next() } catch {} return rightHandSideRuns `), ).toBe(0) }) test("optional deletion short-circuits without evaluating the key", async () => { expect( await value(`let keyReads = 0; const object = null; return [delete object?.[keyReads++], keyReads]`), ).toEqual([true, 0]) }) test("rejects deletion from opaque runtime references", async () => { expect((await error(`return delete tools.example`)).kind).toBe("InvalidDataValue") }) test("keeps blocked property names unavailable", async () => { expect((await error(`const object = {}; return delete object.__proto__`)).kind).toBe("ExecutionFailure") expect((await error(`const values = []; return delete values["constructor"]`)).kind).toBe("ExecutionFailure") }) }) describe("H1: NaN/Infinity flow as intermediates and normalize to null at the boundary", () => { test("guards run instead of the program crashing on a transient NaN", async () => { expect(await value(`return parseInt("abc") || 0`)).toBe(0) expect(await value(`const x = Number("abc"); return Number.isNaN(x) ? 0 : x`)).toBe(0) expect(await value(`const o = {}; o.count = (o.count || 0) + 1; return o.count`)).toBe(1) // average of an empty list, guarded - the classic divide-by-zero that used to throw pre-guard expect(await value(`const a = []; return a.length ? a.reduce((s,x)=>s+x,0)/a.length : 0`)).toBe(0) }) test("a non-finite value becomes null when it leaves CodeMode", async () => { expect(await value(`return 5/0`)).toBeNull() expect(await value(`return 0/0`)).toBeNull() expect(await value(`return Math.max()`)).toBeNull() // nested, too - normalization walks the returned structure expect(await value(`return { a: Number("x"), b: 2, c: [1/0] }`)).toEqual({ a: null, b: 2, c: [null] }) }) test("NaN and Infinity are usable identifiers and inspectable in-CodeMode", async () => { expect(await value(`return Number.isNaN(NaN)`)).toBe(true) expect(await value(`return Infinity > 1e9`)).toBe(true) expect(await value(`return Number.isFinite(1/0)`)).toBe(false) expect(await value(`return [3,1,2].reduce((a,b)=>Math.max(a,b), -Infinity)`)).toBe(3) // JSON.stringify inside CodeMode matches JS: non-finite serializes to null expect(await value(`return JSON.stringify({ x: Number("z") })`)).toBe('{"x":null}') }) test("copyOut normalizes non-finite numbers to null (the shared return + tool-arg boundary)", () => { // Tool-call arguments funnel through copyOut too, so this one function pins both boundaries. expect(ToolRuntime.copyOut(NaN, "json")).toBeNull() expect(ToolRuntime.copyOut(Infinity, "json")).toBeNull() expect(ToolRuntime.copyOut(-Infinity, "nullify")).toBeNull() expect(ToolRuntime.copyOut(42, "json")).toBe(42) expect(ToolRuntime.copyOut({ a: NaN, b: [Infinity, 1] }, "json")).toEqual({ a: null, b: [null, 1] }) }) }) describe("copyOut undefined handling per boundary mode", () => { test("json mode mirrors JSON.stringify for undefined", () => { expect(ToolRuntime.copyOut({ q: undefined, keep: 1 }, "json")).toStrictEqual({ keep: 1 }) expect(ToolRuntime.copyOut([1, undefined, 2], "json")).toStrictEqual([1, null, 2]) expect(ToolRuntime.copyOut({ nested: { a: undefined, b: [undefined] } }, "json")).toStrictEqual({ nested: { b: [null] }, }) expect(ToolRuntime.copyOut(undefined, "json")).toBeUndefined() expect(ToolRuntime.copyOut({ a: undefined }, "nullify")).toStrictEqual({ a: null }) }) }) describe("Error values and instanceof", () => { test("new Error carries name/message and is instanceof Error", async () => { expect(await value(`const e = new Error("boom"); return [e instanceof Error, e.name, e.message]`)).toEqual([ true, "Error", "boom", ]) }) test("Error without new behaves like new Error", async () => { expect(await value(`const e = Error("plain"); return [e instanceof Error, e.name, e.message]`)).toEqual([ true, "Error", "plain", ]) expect(await value(`const e = new Error(); return [e.name, e.message, e instanceof Error]`)).toEqual([ "Error", "", true, ]) }) test("specific error types are instanceof themselves and Error, not each other", async () => { expect( await value( `const e = new TypeError("t"); return [e instanceof TypeError, e instanceof Error, e instanceof RangeError]`, ), ).toEqual([true, true, false]) expect(await value(`return new Error("e") instanceof TypeError`)).toBe(false) }) test("thrown errors keep instanceof through try/catch", async () => { expect(await value(`try { throw new Error("x") } catch (e) { return [e instanceof Error, e.message] }`)).toEqual([ true, "x", ]) }) test("interpreter runtime failures are caught as Error values", async () => { expect(await value(`try { JSON.parse("nope") } catch (e) { return e instanceof Error }`)).toBe(true) expect(await value(`try { undeclared() } catch (e) { return e instanceof Error }`)).toBe(true) }) test("caught failures carry the constructor name the real-JS failure would have", async () => { // JSON.parse throws SyntaxError: name and specific-instanceof both carry through, and the // message keeps the engine's position detail. expect( await value(` try { JSON.parse("{oops") } catch (e) { return [e.name, e instanceof SyntaxError, e instanceof Error, e instanceof TypeError, e.message.includes("JSON")] } `), ).toEqual(["SyntaxError", true, true, false, true]) expect(await value(`try { undeclared() } catch (e) { return [e.name, e instanceof ReferenceError] }`)).toEqual([ "ReferenceError", true, ]) expect(await value(`try { const c = 1; c = 2 } catch (e) { return [e.name, e instanceof TypeError] }`)).toEqual([ "TypeError", true, ]) expect(await value(`try { "a".match("(") } catch (e) { return [e.name, e instanceof SyntaxError] }`)).toEqual([ "SyntaxError", true, ]) expect(await value(`try { new RegExp("(") } catch (e) { return [e.name, e instanceof SyntaxError] }`)).toEqual([ "SyntaxError", true, ]) }) test("diagnostics without a specific real-JS analogue are named plain Error", async () => { expect(await value(`try { JSON.parse(5) } catch (e) { return [e.name, e instanceof Error] }`)).toEqual([ "Error", true, ]) }) test("Promise.allSettled rejection reasons are Error values", async () => { expect( await value(` const settled = await Promise.allSettled([Promise.reject(new Error("b"))]) return [settled[0].reason instanceof Error, settled[0].reason.message] `), ).toEqual([true, "b"]) }) test("non-error thrown values are not instanceof Error", async () => { expect(await value(`try { throw "raw" } catch (e) { return e instanceof Error }`)).toBe(false) expect(await value(`try { throw { message: "shaped" } } catch (e) { return e instanceof Error }`)).toBe(false) }) test("plain data is never instanceof Error", async () => { expect(await value(`return [({}) instanceof Error, "s" instanceof Error, null instanceof Error]`)).toEqual([ false, false, false, ]) }) test("error values still serialize as plain { name, message } data", async () => { expect(await value(`return new Error("m")`)).toEqual({ name: "Error", message: "m" }) expect(await value(`return JSON.stringify(new Error("m"))`)).toBe('{"name":"Error","message":"m"}') expect(await value(`try { throw new Error("m") } catch (e) { return Object.keys(e) }`)).toEqual(["name", "message"]) }) test("spreading an error loses the brand, like losing the prototype in JS", async () => { expect(await value(`const e = new Error("m"); return ({ ...e }) instanceof Error`)).toBe(false) expect(await value(`const e = new Error("m"); return { ...e }`)).toEqual({ name: "Error", message: "m" }) }) test("typeof Error is function; an unknown instanceof right-hand side is a catchable error", async () => { expect(await value(`return typeof Error`)).toBe("function") expect(await value(`try { return 1 instanceof 5 } catch (e) { return "caught" }`)).toBe("caught") const err = await error(`return 1 instanceof 5`) expect(err.message).toContain("right-hand side of 'instanceof'") }) }) describe("CodeMode-specific array behavior", () => { test("sort with a comparator mutates and returns the receiver", async () => { expect( await value(` const input = [3, 1, 2] const result = input.sort((a, b) => a - b) return { input, same: input === result } `), ).toEqual({ input: [1, 2, 3], same: true }) }) test("splice can replace and insert elements", async () => { expect(await value(`const a = ["a","d"]; a.splice(1, 0, "b", "c"); return a`)).toEqual(["a", "b", "c", "d"]) expect(await value(`const a = [1,2,3]; const removed = a.splice(1, 1, "x"); return { removed, a }`)).toEqual({ removed: [2], a: [1, "x", 3], }) }) test("splice rejects inserting a container into itself", async () => { const err = await error(`const a = [1]; a.splice(0, 0, [a]); return a`) expect(err.kind).toBe("InvalidDataValue") expect(err.message).toContain("circular") }) test("keys/values/entries return arrays usable with for...of and spread", async () => { expect(await value(`return [...["x","y","z"].keys()]`)).toEqual([0, 1, 2]) expect(await value(`return ["x","y"].values()`)).toEqual(["x", "y"]) expect( await value(` const out = [] for (const [index, item] of ["a","b"].entries()) out.push(index + ":" + item) return out `), ).toEqual(["0:a", "1:b"]) expect(await value(`return [...[7].entries()]`)).toEqual([[0, 7]]) }) }) describe("CodeMode-specific string behavior", () => { test("localeCompare orders strings for sorting", async () => { expect(await value(`return ["b","a","c"].sort((x, y) => x.localeCompare(y))`)).toEqual(["a", "b", "c"]) }) test("an invalid normalize form is a clear catchable error", async () => { expect(await value(`try { "x".normalize("nope"); return "no" } catch (e) { return e.message }`)).toContain('"NFC"') }) test("does not expose obsolete string aliases", async () => { expect(await value(`return [typeof "x".trimLeft, typeof "x".trimRight, typeof "x".substr]`)).toEqual([ "undefined", "undefined", "undefined", ]) }) }) describe("compound assignment matches its binary operator", () => { // `x op= y` must behave exactly like `x = x op y`, sharing the binary operator's coercion // semantics (Dates string-coerce for `+` and use their time value for arithmetic; data // objects/arrays coerce to their JS string form). const pair = async (compound: string, expanded: string) => { const [a, b] = await Promise.all([value(compound), value(expanded)]) expect(a).toEqual(b) return a } test("CodeMode Date += concatenates its string form, like d = d + 1", async () => { const result = await pair(`let d = new Date(1000); d += 1; return d`, `let d = new Date(1000); d = d + 1; return d`) expect(result).toBe("1970-01-01T00:00:01.000Z1") }) test("CodeMode Date numeric compound ops use its time value", async () => { expect( await pair(`let d = new Date(1000); d -= 400; return d`, `let d = new Date(1000); d = d - 400; return d`), ).toBe(600) expect(await pair(`let d = new Date(1000); d /= 4; return d`, `let d = new Date(1000); d = d / 4; return d`)).toBe( 250, ) }) test("string += object/array matches x = x + obj", async () => { expect(await pair(`let x = "a"; x += { b: 1 }; return x`, `let x = "a"; x = x + { b: 1 }; return x`)).toBe( "a[object Object]", ) expect(await pair(`let x = "a"; x += [1, 2]; return x`, `let x = "a"; x = x + [1, 2]; return x`)).toBe("a1,2") }) test("compound assignment through a member target coerces the same way", async () => { expect( await pair( `const o = { s: "t" }; o.s += new Date(0); return o.s`, `const o = { s: "t" }; o.s = o.s + new Date(0); return o.s`, ), ).toBe("t1970-01-01T00:00:00.000Z") }) test("numeric and string compound operators sweep identically to their expansions", async () => { const cases: Array<[string, number | string]> = [ [`let x = 7; x += 3; return x`, 7 + 3], [`let x = 7; x -= 3; return x`, 7 - 3], [`let x = 7; x *= 3; return x`, 7 * 3], [`let x = 7; x /= 2; return x`, 7 / 2], [`let x = 7; x %= 3; return x`, 7 % 3], [`let x = 7; x **= 2; return x`, 7 ** 2], [`let x = 7; x &= 3; return x`, 7 & 3], [`let x = 7; x |= 8; return x`, 7 | 8], [`let x = 7; x ^= 2; return x`, 7 ^ 2], [`let x = 7; x <<= 2; return x`, 7 << 2], [`let x = -7; x >>= 1; return x`, -7 >> 1], [`let x = -7; x >>>= 1; return x`, -7 >>> 1], [`let x = "a"; x += "b"; return x`, "ab"], ] for (const [compound, expected] of cases) { expect(await value(compound)).toBe(expected) expect(await value(compound.replace(/x (\S+)= /, (_, op) => `x = x ${op} `))).toBe(expected) } }) }) describe("H5: builtin coercion functions work as array callbacks", () => { test("filter(Boolean) drops falsy values", async () => { expect(await value(`return [0, 1, "", 2, null, 3].filter(Boolean)`)).toEqual([1, 2, 3]) }) test("map(String) coerces each element", async () => { expect(await value(`return [1, 2, 3].map(String)`)).toEqual(["1", "2", "3"]) }) test("a non-callable callback is still rejected", async () => { const err = await error(`return [1,2,3].map(42)`) expect(err.message).toContain("callback") }) }) describe("for...of assignment destructuring", () => { test("assigns entry pairs into predeclared variables", async () => { expect( await value(` let key let item const out = [] for ([key, item] of Object.entries({ a: 1, b: 2 })) out.push(key + item) return { key, item, out } `), ).toEqual({ key: "b", item: 2, out: ["a1", "b2"] }) }) test("assigns object patterns and defaults", async () => { expect( await value(` let id let label const labels = [] for ({ id, label = "unknown" } of [{ id: 1 }, { id: 2, label: "two" }]) labels.push(label) return { id, label, labels } `), ).toEqual({ id: 2, label: "two", labels: ["unknown", "two"] }) }) }) describe("sequence expressions", () => { test("evaluate left to right and return the final value", async () => { expect(await value(`let x = 0; const result = (x += 1, x *= 3, x + 2); return { x, result }`)).toEqual({ x: 3, result: 5, }) }) test("support comma-separated for-loop updates", async () => { expect( await value(` const pairs = [] for (let left = 0, right = 3; left < right; left++, right--) pairs.push([left, right]) return pairs `), ).toEqual([ [0, 3], [1, 2], ]) }) }) describe("destructuring assignment", () => { test("assigns object and array patterns to existing bindings", async () => { expect( await value(` let a = 0 let b = 0 ;({ a } = { a: 2 }) ;[a, b] = [3, 4] return [a, b] `), ).toEqual([3, 4]) }) test("supports defaults, nesting, rest, and member targets", async () => { expect( await value(` let first = 0 let fallback = 0 let rest = {} const target = {} ;[first, fallback = 2, ...target.tail] = [1] ;({ nested: { value: target.value }, kept: target.kept = 3, ...rest } = { nested: { value: 4 }, extra: 5, }) return { first, fallback, target, rest } `), ).toEqual({ first: 1, fallback: 2, target: { tail: [], value: 4, kept: 3 }, rest: { extra: 5 } }) }) test("returns the assigned value", async () => { expect(await value(`let a = 0; const result = ([a] = [7]); return [a, result]`)).toEqual([7, [7]]) }) test("supports computed object keys and evaluates them once", async () => { expect( await value(` let calls = 0 const field = () => { calls++; return "name" } const { [field()]: name, ...rest } = { name: "Ada", role: "engineer" } return { calls, name, rest } `), ).toEqual({ calls: 1, name: "Ada", rest: { role: "engineer" } }) }) test("supports object patterns over arrays", async () => { expect( await value(` const { 0: first, length, slice, ...rest } = ["a", "b", "c"] return { first, length, sliced: slice(1), rest } `), ).toEqual({ first: "a", length: 3, sliced: ["b", "c"], rest: { 1: "b", 2: "c" } }) }) test("preserves exact computed property names on arrays", async () => { expect( await value(` const { ["01"]: item, ...rest } = [10, 20] return { missing: item === undefined, rest } `), ).toEqual({ missing: true, rest: { 0: 10, 1: 20 } }) }) test("supports array patterns over strings, Maps, Sets, and URLSearchParams", async () => { expect( await value(` const [letter, ...letters] = "A😀B" const [[mapKey, mapValue]] = new Map([["key", 1]]) const [setFirst, setSecond] = new Set([2, 3]) const [[queryKey, queryValue]] = new URLSearchParams("q=test&page=2") return { letter, letters, mapKey, mapValue, setFirst, setSecond, queryKey, queryValue } `), ).toEqual({ letter: "A", letters: ["😀", "B"], mapKey: "key", mapValue: 1, setFirst: 2, setSecond: 3, queryKey: "q", queryValue: "test", }) }) test("supports iterable patterns in assignment and parameters", async () => { expect( await value(` let first let rest ;[first, ...rest] = new Set([1, 2, 3]) const read = ([[key, value]]) => key + value return { first, rest, entry: read(new Map([["a", 4]])) } `), ).toEqual({ first: 1, rest: [2, 3], entry: "a4" }) }) test("rejects computed keys that are not confined property keys", async () => { const err = await error(`const key = {}; const { [key]: value } = {}`) expect(err.message).toContain("Property key must be a string or number") }) }) describe("coercion parity: zero-argument coercion functions", () => { test("Number() is 0 and String() is empty, unlike their undefined-argument forms", async () => { expect(await value(`return Number()`)).toBe(0) expect(await value(`return String()`)).toBe("") expect(await value(`return Boolean()`)).toBe(false) expect(await value(`return Number.isNaN(Number(undefined))`)).toBe(true) expect(await value(`return String(undefined)`)).toBe("undefined") }) test("parseInt() and parseFloat() stay NaN with no argument", async () => { expect(await value(`return Number.isNaN(parseInt())`)).toBe(true) expect(await value(`return Number.isNaN(parseFloat())`)).toBe(true) }) }) describe("coercion parity: global isFinite and isNaN", () => { test("coerce their argument like native JS, unlike the Number statics", async () => { expect(await value(`return isFinite("42")`)).toBe(true) expect(await value(`return Number.isFinite("42")`)).toBe(false) expect(await value(`return isNaN("oops")`)).toBe(true) expect(await value(`return isNaN("42")`)).toBe(false) expect(await value(`return isFinite(Infinity)`)).toBe(false) expect(await value(`return isNaN(null)`)).toBe(false) }) test("zero-argument forms match native", async () => { expect(await value(`return isFinite()`)).toBe(false) expect(await value(`return isNaN()`)).toBe(true) }) test("read as functions", async () => { expect(await value(`return typeof isFinite`)).toBe("function") expect(await value(`return typeof isNaN`)).toBe("function") }) test("work as array callbacks", async () => { expect(await value(`return [1, "2", "x", Infinity].filter(isFinite)`)).toEqual([1, "2"]) expect(await value(`return ["1", "x"].map(isNaN)`)).toEqual([false, true]) }) }) describe("coercion parity: arrays coerce to numbers through their string form", () => { test("arrays with objects become NaN instead of crashing on host ToPrimitive", async () => { expect(await value(`let x = [{}]; x++; return Number.isNaN(x)`)).toBe(true) expect(await value(`return isFinite([{}])`)).toBe(false) expect(await value(`return "abc".slice([{}])`)).toBe("abc") }) test("single-element and empty arrays match native Number()", async () => { expect(await value(`return Number([5])`)).toBe(5) expect(await value(`return Number([])`)).toBe(0) expect(await value(`return Number.isNaN(Number([1, 2]))`)).toBe(true) }) }) describe("coercion parity: String method arguments coerce like native JS", () => { test("includes and indexOf coerce numbers", async () => { expect(await value(`return "v1.2".includes(1)`)).toBe(true) expect(await value(`return "a2b".indexOf(2)`)).toBe(1) expect(await value(`return "abc".includes("d")`)).toBe(false) }) test("slice, repeat, and padStart coerce numeric strings", async () => { expect(await value(`return "abc".slice("1")`)).toBe("bc") expect(await value(`return "ab".repeat("2")`)).toBe("abab") expect(await value(`return "7".padStart("3", 0)`)).toBe("007") }) test("split coerces separators but treats undefined as absent", async () => { expect(await value(`return "a1b".split(1)`)).toEqual(["a", "b"]) expect(await value(`return "a,b".split(undefined)`)).toEqual(["a,b"]) expect(await value(`return "a,b".split()`)).toEqual(["a,b"]) expect(await value(`return "a,b".split(undefined, 0)`)).toEqual([]) expect(await value(`return "a,b".split(undefined, 1)`)).toEqual(["a,b"]) }) test("replace coerces search and replacement values", async () => { expect(await value(`return "a1b".replace(1, 2)`)).toBe("a2b") expect(await value(`return "a1b".replace(1, () => "x")`)).toBe("axb") }) test("repeat rejections carry the native RangeError name", async () => { expect(await value(`try { "a".repeat(-1) } catch (e) { return e.name }`)).toBe("RangeError") }) test("includes, startsWith, and endsWith reject regular expressions with a TypeError", async () => { expect(await value(`try { "abc".includes(/a/) } catch (e) { return e.name }`)).toBe("TypeError") expect(await value(`try { "abc".startsWith(/a/) } catch (e) { return e.name }`)).toBe("TypeError") expect(await value(`try { "abc".endsWith(/a/) } catch (e) { return e.name }`)).toBe("TypeError") }) test("opaque runtime references still reject as data errors", async () => { const err = await error(`const f = () => 1; return "abc".includes(f)`) expect(err.message).toContain("data value") const replacerErr = await error(`const f = () => 1; return "a".replace(f, () => "x")`) expect(replacerErr.message).toContain("data value") }) }) describe("coercion parity: match() and search() with no argument", () => { test("behave as an empty pattern like native JS", async () => { expect(await value(`return "abc".search()`)).toBe(0) expect(await value(`const m = "abc".match(); return { first: m[0], index: m.index }`)).toEqual({ first: "", index: 0, }) }) }) describe("coercion parity: ++ and -- use CodeMode numeric coercion", () => { test("numeric strings increment like native JS", async () => { expect(await value(`let x = "5"; x++; return x`)).toBe(6) expect(await value(`let x = "5"; return ++x`)).toBe(6) expect(await value(`const o = { n: "2" }; o.n--; return o.n`)).toBe(1) }) test("dates increment through their epoch time", async () => { expect(await value(`let d = new Date(5); d++; return d`)).toBe(6) }) test("plain data objects become NaN instead of crashing", async () => { expect(await value(`let x = {}; x++; return Number.isNaN(x)`)).toBe(true) expect(await value(`const o = { a: {} }; o.a++; return Number.isNaN(o.a)`)).toBe(true) }) test("opaque runtime references reject with a clear error", async () => { const err = await error(`let f = () => 1; f++`) expect(err.message).toContain("data value") }) }) describe("coercion parity: unknown static members read as undefined", () => { test("feature detection on missing statics works like native JS", async () => { expect(await value(`return typeof Math.sumPrecise`)).toBe("undefined") expect(await value(`return Object.groupBy === undefined`)).toBe(true) expect(await value(`return RegExp.escape === undefined`)).toBe(true) expect(await value(`return Number.range === undefined`)).toBe(true) expect(await value(`return String.raw === undefined`)).toBe(true) expect(await value(`return isFinite.something === undefined`)).toBe(true) expect(await value(`return console.group === undefined`)).toBe(true) expect(await value(`return Date.moment === undefined`)).toBe(true) expect(await value(`return JSON.rawJSON === undefined`)).toBe(true) expect(await value(`return URL.createObjectURL === undefined`)).toBe(true) expect(await value(`return Map.groupBy === undefined`)).toBe(true) expect(await value(`return Math.sumPrecise?.([1]) ?? "fallback"`)).toBe("fallback") }) test("known statics still resolve and run", async () => { expect(await value(`return typeof Math.max`)).toBe("function") expect(await value(`return typeof console.log`)).toBe("function") expect(await value(`return typeof Date.now`)).toBe("function") expect(await value(`return Math.max(1, 2)`)).toBe(2) expect(await value(`return URL.canParse("https://example.com")`)).toBe(true) expect(await value(`return Number.isInteger(3)`)).toBe(true) expect(await value(`return Number.MAX_SAFE_INTEGER`)).toBe(Number.MAX_SAFE_INTEGER) }) test("calling an unknown static reports a native-style TypeError", async () => { expect(await value(`try { Math.sumPrecise([1]) } catch (e) { return e.name + ": " + e.message }`)).toBe( "TypeError: Math.sumPrecise is not a function.", ) expect(await value(`try { Math["sumPrecise"]([1]) } catch (e) { return e.message }`)).toBe( "Math.sumPrecise is not a function.", ) }) test("blocked members still throw instead of reading as undefined", async () => { const err = await error(`return Math.constructor`) expect(err.message).toContain("not available") const coercionErr = await error(`return Number.constructor`) expect(coercionErr.message).toContain("Number.constructor is not available") }) })