constructor(init) {
		// Validate and normalize init object in [name, value(s)][]
		/** @type {string[][]} */
		let result = [];
		if (init instanceof Headers) {
			const raw = init.raw();
			for (const [name, values] of Object.entries(raw)) {
				result.push(...values.map(value => [name, value]));
			}
		} else if (init == null) { // eslint-disable-line no-eq-null, eqeqeq
			// No op
		} else if (typeof init === 'object' && !types.isBoxedPrimitive(init)) {
			const method = init[Symbol.iterator];
			// eslint-disable-next-line no-eq-null, eqeqeq
			if (method == null) {
				// Record<ByteString, ByteString>
				result.push(...Object.entries(init));
			} else {
				if (typeof method !== 'function') {
					throw new TypeError('Header pairs must be iterable');
				}

				// Sequence<sequence<ByteString>>
				// Note: per spec we have to first exhaust the lists then process them
				result = [...init]
					.map(pair => {
						if (
							typeof pair !== 'object' || types.isBoxedPrimitive(pair)
						) {
							throw new TypeError('Each header pair must be an iterable object');
						}

						return [...pair];
					}).map(pair => {
						if (pair.length !== 2) {
							throw new TypeError('Each header pair must be a name/value tuple');
						}

						return [...pair];
					});
			}
		} else {
			throw new TypeError('Failed to construct \'Headers\': The provided value is not of type \'(sequence<sequence<ByteString>> or record<ByteString, ByteString>)');
		}

		// Validate and lowercase
		result =
			result.length > 0 ?
				result.map(([name, value]) => {
					validateHeaderName(name);
					validateHeaderValue(name, String(value));
					return [String(name).toLowerCase(), String(value)];
				}) :
				undefined;

		super(result);

		// Returning a Proxy that will lowercase key names, validate parameters and sort keys
		// eslint-disable-next-line no-constructor-return
		return new Proxy(this, {
			get(target, p, receiver) {
				switch (p) {
					case 'append':
					case 'set':
						return (name, value) => {
							validateHeaderName(name);
							validateHeaderValue(name, String(value));
							return URLSearchParams.prototype[p].call(
								target,
								String(name).toLowerCase(),
								String(value)
							);
						};

					case 'delete':
					case 'has':
					case 'getAll':
						return name => {
							validateHeaderName(name);
							return URLSearchParams.prototype[p].call(
								target,
								String(name).toLowerCase()
							);
						};

					case 'keys':
						return () => {
							target.sort();
							return new Set(URLSearchParams.prototype.keys.call(target)).keys();
						};

					default:
						return Reflect.get(target, p, receiver);
				}
			}
		});
		/* c8 ignore next */
	}
Headers class

@constructor
@param {HeadersInit} [init] - Response headers