exp-fetch

fetch

A small and pluggable lib to fetch a resource and cache the result.

Caching

Fetch will parse the cache-control header. If fetch encounters private, no-cache, max-age=0 or must-revalidate it wont cache. Otherwise it will respect the max-age header.

Callback usage:

var behavior = {};
var fetch = fetchBuilder(behavior);
fetch("http://example.com/resource.json", function (err, content) {
    // Do something with the result
});

Promise usage:

var behavior = {};
var fetch = fetchBuilder(behavior);
fetch("http://example.com/resource.json").then(function (content) {
    // Do something with the result
});

Allowed behavior options

• freeze: (default:false). When this option is set it will freeze the response so it can't be modified.
• cache: (default: an instance of AsyncCache) (https://github.com/ExpressenAB/exp-asynccache). To disable caching set {cache: null}
• cacheKeyFn: (default: caches on the url) An optional formatting function for finding the cache-key. One might, for example, want to cache on an url with the get params stripped.
• maxAgeFn: (default: respects the cache-control header)
• onNotFound: If given a function, it will be called each time fetch encounters a 404
• onError: If given a function, it will be called each time fetch encounters a non 200 nor 404 response
• onSuccess: If given a function, it will be called each time fetch encounters a 200
• logger: A logger object implementing error, warning, info, debug for example https://github.com/tj/log.js
• cacheNotFound: (default: false). If set it will cache 404s, if given a number it will cache the 404 for that time. If the maxAgeFn is given, it will get this time as the first parameter.

CacheKeyFn

var keyFinder = function (url) {
    return url.replace(/\//g, "");
}
var fetch = fetchBuilder({cacheKeyFn: keyFinder});
Promise.all([
   fetch("http://example.com/foo/bar")
   fetch("http://example.com/foobar")
]).then(function (result) {
   result[0] === result[1];
});

maxAgeFn

function cacheNothing(maxAge, key, res, content) {
    return -1;
}
var fetch = fetchBuilder({maxAgeFn: cacheNothing});

Init cache function

The fetch lib provides a convenient initCache-method which sets up a cache purging it's expired content.

var initCache = require("exp-fetch").initCache;
var cache = new AsyncCache(initCache({ age: 60, size: 2000});

Allowed params:

• size or max: the max allowed size, the unit is set by the length method. Default is value.length. Default: 2000000
• length: the length function, default is v && v.length || 1
• age or maxAge: the maximum number of seconds a key will be kept in the cache. Default 60