@civic/simple-cache

A function that produces a cached version of the input function, where, similarly to _.memoize, function calls with the same parameters will be cached and returned.

Unlike _.memoize, the cached values will expire after ttl milliseconds (default 1hr)

const cache = require('simple-cache');

function slowRarelyChangingFunction(a, b) {
  ...
}

const cachedFn = cache(slowRarelyChangingFunction, { ttl: <ttl in ms>})
const result1 = cachedFn(1, 2); // cache miss - slow
const result2 = cachedFn(3, 4); // cache miss - slow
const result3 = cachedFn(1, 2); // cache hit - fast

The underlying cache is available at cachedFn.cache.

The results are stored in the cache as follows:

JSON.stringify(decycle(arguments)) -> result

The arguments are stringified in order to allow subsequent lookups on argument lists that have the same contents, but are not equal in terms of JS equality (===).

To avoid problems with stringification, the arguments are decycled first using the json-cycle library.

This process has two important side-effects:

Note 1: The decycling and stringification can be expensive - so this cache should not be used for complex object inputs (e.g. large DOM trees) Note 2: Since WeakMap does not allow String keys, we use Map here. This can lead to memory leaks if a service runs for a long time.

To mitigate memory leaks, the function provides access to the underlying cache via cachedFn.cache. You can clear the cache by calling:

cachedFn.cache = new Map();

or you can pass any implementation you like of the Map interface, in order to control the cache size.

You can also manipulate the arguments before they get stringified, for example, in order to remove arguments that are not suitable to be used as a cache key.

const negate = (a, logger) => {
    logger.log(a);
    return !a
}
const ignoreSecondArgument = cache(negate, { convertArgFn: a => a });