		{
		"name": "expired",
		"version": "0.1.0",
		"description": "Calculate when HTTP cache headers expire",
		"version": "1.0.0",
		"description": "Calculate when HTTP responses expire from the cache headers",
		"main": "src/index.js",
		@@ -16,8 +16,10 @@ "scripts": {
		"keywords": [
		"calculate",
		"HTTP",
		"response",
		"expires",
		"expire",
		"expirey",
		"cache",
		"headers",
		"expire",
		"expires",
		"expirey"
		"headers"
		],
		@@ -31,3 +33,4 @@ "author": "Luke Childs <lukechilds123@gmail.com> (http://lukechilds.co.uk)",
		"dependencies": {
		"date-fns": "^1.21.1"
		"date-fns": "1.21.1",
		"parse-headers": "2.0.1"
		},
		@@ -37,5 +40,7 @@ "devDependencies": {
		"coveralls": "^2.11.15",
		"date-fns": "^1.21.1",
		"nyc": "^10.0.0",
		"timekeeper": "^1.0.0",
		"xo": "^0.17.1"
		}
		}

src/index.js

		const isPast = require('date-fns/is_past');
		const differenceInMilliseconds = require('date-fns/difference_in_milliseconds');
		const addSeconds = require('date-fns/add_seconds');
		const parse = require('parse-headers');

		// Returns boolean for whether or not the cache has expired
		const expired = headers => isPast(expired.on(headers));

		// Return ms until cache expires
		expired.in = headers => differenceInMilliseconds(expired.on(headers), new Date());

		// Returns date when cache will expire
		expired.on = headers => {
		// Parse headers if we got a raw string
		headers = (typeof headers === 'string') ? parse(headers) : headers;

		// Date from headers
		const originDate = new Date(headers.date);

		// Get max age ms
		// Get max age ms
		let maxAge = headers['cache-control'] && headers['cache-control'].match(/max-age=(\d+)/);
		maxAge = parseInt(maxAge ? maxAge[1] : 0, 10);

		// Take current age into account
		// Take current age into account
		if (headers.age) {
		@@ -18,6 +29,6 @@ maxAge -= headers.age;

		// Calculate expirey date
		return addSeconds(new Date(originDate), maxAge);
		// Calculate expirey date
		return addSeconds(originDate, maxAge);
		};

		module.exports = expired;

test/expired.js

		import test from 'ava';
		import subSeconds from 'date-fns/sub_seconds';
		import expired from '../';
		@@ -7,1 +8,21 @@
		});

		test('expired returns false for valid cache', t => {
		const headers = {
		date: new Date().toUTCString(),
		age: 0,
		'cache-control': 'public, max-age=300'
		};

		t.false(expired(headers));
		});

		test('expired returns true for stale cache', t => {
		const headers = {
		date: subSeconds(new Date().toUTCString(), 500),
		age: 0,
		'cache-control': 'public, max-age=300'
		};

		t.true(expired(headers));
		});

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