mirror of
https://github.com/vercel-labs/scriptc.git
synced 2026-11-02 07:43:42 +08:00
Chris Tate
e00d3fd911
- The assert comparison methods read as function values (equal, strictEqual, deepEqual, partialDeepStrictEqual and their negations) throw Node's ERR_MISSING_ARGS TypeError, `The "actual" and "expected" arguments must be specified`, when called with fewer than two arguments, where `[assert.equal][0]()` passed. - Untyped `instanceof Object` starts at the value's prototype, so Object.prototype itself, whose prototype is null, is not an Object. - Untyped `instanceof Function` follows the whole prototype chain through objects and functions: an object whose prototype is a function, or a function whose prototype was set to such an object, is a Function.
78 lines
2.5 KiB
JavaScript
78 lines
2.5 KiB
JavaScript
'use strict';
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// `x instanceof Object` and `x instanceof Function` on untyped values follow
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// Node: objects are instances of Object unless their prototype chain ends
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// in null first, and functions (classes and arrows included) are instances
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// of Function.
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class Shape {}
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class Square extends Shape {}
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const nullProto = Object.create(null);
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const underNull = Object.create(nullProto);
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const regrown = Object.create(null);
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Object.setPrototypeOf(regrown, {});
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const orphan = function orphan() {};
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Object.setPrototypeOf(orphan, null);
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function declared() {}
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const values = {
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'plain object': {},
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array: [1, 2],
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'Object.create(null)': nullProto,
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'object under a null-prototype object': underNull,
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'Object.create(null) given a prototype': regrown,
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'Object.create(plain object)': Object.create({ a: 1 }),
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'parsed JSON': JSON.parse('{"a":[1]}'),
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'function declaration': declared,
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'bound function': declared.bind(null),
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'arrow function': () => 1,
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'async function': async () => {},
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class: Square,
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'class instance': new Square(),
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'function with a null prototype': orphan,
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map: new Map(),
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date: new Date(0),
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'regular expression': /x/,
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error: new TypeError('t'),
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'typed array': new Uint8Array(2),
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promise: Promise.resolve(1),
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number: 1,
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string: 's',
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boolean: false,
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null: null,
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undefined: undefined,
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symbol: Symbol('s'),
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bigint: 10n,
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};
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for (const [label, value] of Object.entries(values)) {
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console.log(`${label}: Object ${value instanceof Object}, Function ${value instanceof Function}`);
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}
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function describe(value) {
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if (!(value instanceof Object)) return 'primitive or null-prototype';
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return value instanceof Function ? 'function' : 'object';
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}
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console.log([nullProto, {}, describe, 0].map(describe).join(', '));
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// Prototype chains through functions and objects, and Object.prototype
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// itself, whose own prototype is null.
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const base = function base() {};
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const fromFunction = {};
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Object.setPrototypeOf(fromFunction, base);
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const throughObject = {};
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Object.setPrototypeOf(throughObject, fromFunction);
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const nullRooted = function nullRooted() {};
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Object.setPrototypeOf(nullRooted, null);
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const reparented = function reparented() {};
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Object.setPrototypeOf(reparented, fromFunction);
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const chains = {
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objectPrototype: Object.getPrototypeOf({}),
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fromFunction,
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throughObject,
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nullRooted,
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reparented,
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};
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for (const [label, value] of Object.entries(chains)) {
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console.log(`${label}: Object ${value instanceof Object}, Function ${value instanceof Function}`);
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}
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