cached-decorator

@Cached decorator for TypeScript

This library provides a mechanism to selectively cache (memoize) method calls.

Installing

To install the library issue the following command:

$ npm install --save cached-decorator

Types are provided with the package

Using the library

To use the library, in its simplest form, you add the @Cached() decorator to a method in classes like this:

class Calculator {
  @Cached()
  sum(x: number, y: number): number {
    console.log('Calculating sum')
    return x + y
  }
}

const calc = new Calculator()
calc.sum(1, 2)
calc.sum(1, 2)
calc.sum(1, 2)

Upon running you will notice that the log "Calculating sum" is called only once.

Specifying timeout for cached values

It is possible that sometimes you'll want to have a time-constrained version of the cache. You can specify how long will it take for a certain result of method call is cached by specifying the timeout in milliseconds as the first parameter of the decorator:

class Calculator {
  @Cached(1000)
  sum(x: number, y: number): number {
    ...

The above change will cache the result of the call to sum for 1 second.

Specifying a different implementation for caching

It is possible to tweak how the library works by specifying cache implementation and its parameters. There are two main implementations:

MemoryCache - this cache is implemented using a nested Map construct. It has a destroy() method that will release all the allocated resources

ObjectCache - this cache implementation hooks up to the instance of the class, creates the __cache__ key and stores the values there.

Both implementations expect the following optional parameters:

timeout - after the specified time the cached entry will be invalidated and removed from cache (default: Number.POSITIVE_INFINITY)

updateOnGet - refresh key's time when fetching (default: false)

Here's an example of how to use ObjectCache implementation with 1 second timeout and refreshing the key's age on every call to the function:

class Calculator {
  @Cached(, new ObjectCache(1000, true))
  sum(x: number, y: number): number {
    ...

The timeout parameter is by default just passed on to the constructor of MemoryCache (default cache implementation) - hence it needs to be skipped when using this decorator.