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MIRROR: javascript for 🐜's, a tiny runtime with big ambitions ant.themackabu.dev
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12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626364656667686970717273747576const assert = require('node:assert');const { EventEmitter } = require('node:events');
function throwsExactly(fn, reason, label) { let caught = false; try { fn(); } catch (error) { caught = true; assert.strictEqual(error, reason, label); } assert.ok(caught, `${label}: missing throw`);}
for (const reason of [undefined, null, new Error('original')]) { const emitter = new EventEmitter(); let laterCalls = 0; emitter.once('event', () => { throw reason; }); emitter.on('event', () => laterCalls++); throwsExactly(() => emitter.emit('event'), reason, 'emit'); assert.strictEqual(laterCalls, 0); assert.strictEqual(emitter.emit('event'), true); assert.strictEqual(laterCalls, 1, 'once listener must be removed even after throwing');
for (const Ctor of [Map, Set, WeakMap, WeakSet, Headers, Blob]) { for (const stage of ['open', 'next', 'done', 'value']) { let closed = 0; const source = { [Symbol.iterator]() { return this; }, next() { if (stage === 'next') throw reason; return { get done() { if (stage === 'done') throw reason; return false; }, get value() { throw reason; }, }; }, return() { closed++; return {}; }, }; if (stage === 'open') Object.defineProperty(source, Symbol.iterator, { get() { throw reason; } }); throwsExactly(() => new Ctor(source), reason, `${Ctor.name} ${stage}`); assert.strictEqual(closed, 0, 'a failed iterator step must not call return'); } }
for (const stage of ['next', 'done', 'value']) { let mapped = 0; const source = { next() { return { get done() { if (stage === 'done') throw reason; return false; }, get value() { throw reason; }, }; } }; if (stage === 'next') Object.defineProperty(source, 'next', { get() { throw reason; } }); throwsExactly(() => Iterator.prototype.map.call(source, () => mapped++).next(), reason, `iterator ${stage}`); assert.strictEqual(mapped, 0); }
for (const field of ['wasClean', 'code', 'reason']) { const init = {}; Object.defineProperty(init, field, { get() { throw reason; } }); throwsExactly(() => new CloseEvent('close', init), reason, `CloseEvent ${field}`); } let reasonRead = false; throwsExactly(() => new CloseEvent('close', { code: { valueOf() { throw reason; } }, get reason() { reasonRead = true; return ''; }, }), reason, 'CloseEvent code conversion'); assert.strictEqual(reasonRead, false); throwsExactly(() => new CloseEvent('close', { reason: { toString() { throw reason; } } }), reason, 'CloseEvent reason conversion');}
for (const globalName of ['RegExp', 'String']) { const descriptor = Object.getOwnPropertyDescriptor(globalThis, globalName); let reads = 0; Object.defineProperty(globalThis, globalName, { configurable: true, get() { reads++; throw new Error('guard getter'); } }); try { assert.strictEqual(/x/.exec('x')[0], 'x'); assert.strictEqual('x'.replace(/x/, 'y'), 'y'); assert.strictEqual(reads, 0, 'optimization guard invoked a global getter'); } finally { Object.defineProperty(globalThis, globalName, descriptor); }}queueMicrotask(() => console.log('Native completion errors ok'));