promiseResolve

/**
 * @param {unknown} value
 * @returns {Promise<unknown>}
 */
export default function promiseResolve(value) {
	// If it's already a native Promise, return it unchanged.
	if (value instanceof Promise) {
		return value;
	}

	// Thenables are objects/functions with a callable `then` method.
	if (
		value !== null &&
		(typeof value === 'object' || typeof value === 'function')
	) {
		const then = value.then;
		if (typeof then === 'function') {
			// Adopt the thenable's eventual state (fulfillment or rejection).
			return new Promise((resolve, reject) => {
				let called = false;

				try {
					then.call(
						value,
						(resolvedValue) => {
							// Guard against thenables that try to settle multiple times.
							if (called) {
								return;
							}
							called = true;
							resolve(resolvedValue);
						},
						(reason) => {
							// Guard against thenables that try to settle multiple times.
							if (called) {
								return;
							}
							called = true;
							reject(reason);
						},
					);
				} catch (error) {
					// If calling `then` throws before settlement, reject with that error.
					if (!called) {
						reject(error);
					}
				}
			});
		}
	}

	// Non-thenable values are wrapped in an already-fulfilled Promise.
	return Promise.resolve(value);
}