Script and results for testing casting of ECMAScript standard defined types to booleans with Boolean() and !!

boolean-test-results.log

✅ Casting "" (type: string) with Boolean() === false
✅ Casting "" (type: string) with !! === false
✅ Casting "a" (type: string) with Boolean() === true
✅ Casting "a" (type: string) with !! === true
✅ Casting 0 (type: number) with Boolean() === false
✅ Casting 0 (type: number) with !! === false
✅ Casting 0.5 (type: number) with Boolean() === true
✅ Casting 0.5 (type: number) with !! === true
✅ Casting 9007199254740992 (type: bigint) with Boolean() === true
✅ Casting 9007199254740992 (type: bigint) with !! === true
✅ Casting Symbol(symbol) (type: symbol) with Boolean() === true
✅ Casting Symbol(symbol) (type: symbol) with !! === true
✅ Casting true (type: boolean) with Boolean() === true
✅ Casting true (type: boolean) with !! === true
✅ Casting false (type: boolean) with Boolean() === false
✅ Casting false (type: boolean) with !! === false
✅ Casting null (type: object) with Boolean() === false
✅ Casting null (type: object) with !! === false
✅ Casting undefined (type: undefined) with Boolean() === false
✅ Casting undefined (type: undefined) with !! === false
✅ Casting {} (type: object) with Boolean() === true
✅ Casting {} (type: object) with !! === true
✅ Casting [] (type: object) with Boolean() === true
✅ Casting [] (type: object) with !! === true
✅ Casting function () {} (type: function) with Boolean() === true
✅ Casting function () {} (type: function) with !! === true

boolean-tests.js

const testCases = [
	// String (empty)
	{ value: "", expectation: false },
	// String
	{ value: "a", expectation: true },
	// Number (integer)
	{ value: 0, expectation: false },
	// Number (floating point)
	{ value: 0.5, expectation: true },
	// BigInt
	{ value: 9007199254740992n, expectation: true },
	// Symbol
	{ value: Symbol("symbol"), expectation: true },
	// Boolean
	{ value: true, expectation: true },
	// Boolean
	{ value: false, expectation: false },
	// null
	{ value: null, expectation: false },
	// undefined
	{ value: undefined, expectation: false },
	// Object
	{ value: {}, expectation: true },
	// Object
	{ value: [], expectation: true },
	// Function
	{ value: function () {}, expectation: true },
];

function outputTestResult({ result, value, expectation, strategy }) {
	const resultIcon = result === true ? "✅" : "❌";

	let valueString = value ? value.toString() : value;
	if (["string", "object", "array"].includes(typeof value)) {
		valueString = JSON.stringify(value);
	}

	console.log(
		`${resultIcon} Casting ${valueString} (type: ${typeof value}) with ${strategy} === ${expectation.toString()}`
	);
}

for (let { value, expectation } of testCases) {
	outputTestResult({
		result: Boolean(value) === expectation,
		value,
		expectation,
		strategy: "Boolean()",
	});

	outputTestResult({
		result: !!value === expectation,
		value,
		expectation,
		strategy: "!!",
	});
}