op-cache

A simple Map based cache with optional persistence.

npm i op-cache

• Usage
• API
• Caveats

Usage

const OPCache = require("op-cache");

// If it does not exist, creates /path/to/cache/file
const cache = new OPCache({
  path: "/path/to/cache/file"
})

cache.set("foo", "bar");

cache.get("foo"); // "bar"

cache.set("hello", "world", true); // Persist key value pair

cache.delete("foo"); // true

cache.delete("hello", false)// Do not persist deletion
// same as
cache.delete("hello");

cache.has("hello"); // false

// Since 'path' exists, newCache will be loaded with the data inside the cache file.
const newCache = new OPCache({
  path: "/path/to/cache/file"
)}

newCache.has("hello"); // true

newCache.clear(true); // Clear cache with persistence (deletes cache file);

const key1 = Symbol("foo");
const key2 = Symbol("foo");

newCache // 'set' calls are chainable
  .set(123, "saved", true) // Can use numbers as keys, this pair will be persisted.
  .set(key1, { foo: "bar" }); // Can use symbols as keys, this pair will *not* be persisted.
  .set(key2, { bar: "baz" }, true); // Values can be any arbitrary value. This pair will be persisted.

API

Methods

.get(key)

Returns a specified element from a the cache. If the value that is associated to the provided key is an object, then you will get a reference to that object and any change made to that object will effectively modify it inside the cache.

.set(key, value, persist = false)

Adds or updates an element with a specified key and a value to the cache. Pass true as a 3rd argument to persist the cached element.

.delete(key, persist = false)

Removes the specified element from a Map object by key. Returns a boolean indicating whether the removal was successful or not. Pass true as a 2nd argument to persist the deletion.

.clear(persist = false)

Removes all elements from the cache. Pass true as an argument remove the cache file.

.persist()

Forcibly re-writes all previously persisted keys to the cache file.

.has(key)

Returns a boolean indicating whether an element with the specified key exists or not.

.entries()

Returns an Iterator that contas the [key, values] pairs for each element in the cache in insertion order.

.keys()

Returns an Iterator that contains the keys for each element in the cache in insertion order.

.values()

Returns an Iterator that contains the values for each element in the cache in insertion order.

Properties

.size

Returns the number of elements in the cache.

Caveats

• While both keys and values can be of any type, persisted elements must be JSON-serializeable in order to be retrieved. This essentially limits you to using the following types for persisted data: string, number, boolean and objects containing exlcuisvely primitive values. Example:

// GOOD

const cache = new OPCache({
    path: "/path/to/cache/file",
});

cache.set("foo", { bar: "baz" }, true);

const newCache = new OPCache({
    path: "/path/to/cache/file",
});

newCache.get("foo"); // { bar: "baz" }

// BAD

const cache = new OPCache({
    path: "/path/to/cache/file",
});

cache.set("sum", (a, b) => a + b, true);

// Note that the element will be available in memory.
const sum = cache.get("sum");
sum(1, 2); // 3;

const newCache = new OPCache({
    path: "/path/to/cache/file",
});

newCache.get("sum"); // undefined

• Persisted keys that are objects will not be directly retrievable until refrencnce to the object is obtained. Example:

const cache = new OPCache({
    path: "/path/to/cache/file",
});

cache.set({ someKey: "someVal" }, "YAY", true);

const newCache = new OPCache({
    path: "/path/to/cache/file",
});

cache.get({ someKey: "someVal" }); // undefined

const objWithReference = Array.from(cache.keys())[0];
cache.get(objWithReference); // "YAY"