Calculate when HTTP cache headers expire
JavaScript
Latest commit 119a7c5 Jan 17, 2017 @lukechilds 1.3.4

README.md

expired

Calculate when HTTP responses expire from the cache headers

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expired accepts HTTP headers as an argument and will return information on when the resource will expire. Cache-Control and Expires headers are supported, if both exist Cache-Control takes priority (Why?).

Install

npm install --save expired

Usage

const expired = require('expired');

const headers = `
Age: 0
Cache-Control: public, max-age=300
Content-Encoding: gzip
Content-Type: application/json;charset=utf-8
Date: Fri, 23 Dec 2016 05:50:31 GMT
Last-Modified: Fri, 23 Dec 2016 05:23:23 GMT`;

expired(headers);
// false

expired.in(headers);
// 500000

expired.on(headers);
// Date('2016-12-23T05:55:31.000Z')

delay(600000).then(() => {

  expired(headers);
  // true

  expired.in(headers);
  // -100000

  expired.on(headers);
  // Date('2016-12-23T05:55:31.000Z')

});

Many HTTP modules will parse response headers into an object for you. expired will also accept headers in this format:

const expired = require('expired');

const headers = {
  'age': '0',
  'cache-control': 'public, max-age=300',
  'content-encoding': 'gzip',
  'content-type': 'application/json;charset=utf-8',
  'date': 'Fri, 23 Dec 2016 05:50:31 GMT',
  'last-modified': 'Fri, 23 Dec 2016 05:23:23 GMT'
};

expired(headers);
// false

Pure Usage

You can make the functions pure by passing in a JavaScript Date object to compare to instead of depending on new Date(). This isn't necessary for expired.on as it doesn't compare dates and is already pure.

The following are all pure functions:

const headers = `...`;
const date = new Date();

expired(headers, date);
expired.in(headers, date);
expired.on(headers);

API

expired(headers, [date])

Returns a boolean relating to whether the resource has expired or not. true means it's expired, false means it's fresh.

expired.in(headers, [date])

Returns the amount of milliseconds from the current date until the resource will expire. If the resource has already expired it will return a negative integer.

expired.on(headers)

Returns a JavaScript Date object for the date the resource will expire.

License

MIT © Luke Childs