constructor() {
		let init = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : undefined;

		this[MAP$5] = Object.create(null);

		if (init instanceof Headers) {
			const rawHeaders = init.raw();
			const headerNames = Object.keys(rawHeaders);

			for (const headerName of headerNames) {
				for (const value of rawHeaders[headerName]) {
					this.append(headerName, value);
				}
			}

			return;
		}

		// We don't worry about converting prop to ByteString here as append()
		// will handle it.
		if (init == null) ; else if (typeof init === 'object') {
			const method = init[Symbol.iterator];
			if (method != null) {
				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
				const pairs = [];
				for (const pair of init) {
					if (typeof pair !== 'object' || typeof pair[Symbol.iterator] !== 'function') {
						throw new TypeError('Each header pair must be iterable');
					}
					pairs.push(Array.from(pair));
				}

				for (const pair of pairs) {
					if (pair.length !== 2) {
						throw new TypeError('Each header pair must be a name/value tuple');
					}
					this.append(pair[0], pair[1]);
				}
			} else {
				// record<ByteString, ByteString>
				for (const key of Object.keys(init)) {
					const value = init[key];
					this.append(key, value);
				}
			}
		} else {
			throw new TypeError('Provided initializer must be an object');
		}
	}
Headers class

@param   Object  headers  Response headers
@return  Void