memo-decorator

Memo Decorator

This decorator applies memoization to a method of a class.

Usage

Apply the decorator to a method of a class. The cache is local for the method but shared among all instances of the class. Strongly recommend you to use this decorator only on pure methods.

Installation:

npm i memo-decorator --save

Configuration

export interface Config {
  resolver?: Resolver;
  cache?: MapLike;
}

• Resolver is a function, which returns the key to be used for given set of arguments. By default, the resolver will use the first argument of the method as the key.
• MapLike is a cache instance. By default, the library would use Map.

Example:

import memo from 'memo-decorator';

class Qux {
  @memo({
    resolver: (...args: any[]) => args[1],
    cache: new WeakMap()
  })
  foo(a: number, b: number) {
    return a * b;
  }
}

Demo

import memo from 'memo-decorator';

class Qux {
  @memo()
  foo(a: number) {
    console.log('foo: called');
    return 42;
  }

  @memo({
    resolver: _ => 1
  })
  bar(a: number) {
    console.log('bar: called');
    return 42;
  }
}

const a = new Qux();
// Create a new cache entry and associate `1` with the result `42`.
a.foo(1);
// Do not invoke the original method `foo` because there's already a cache
// entry for the key `1` associated with the result of the method.
a.foo(1);
// Invoke the original `foo` because the cache doesn't contain an entry
// for the key `2`.
a.foo(2);

// Invoke `bar` and return the result `42` gotten from the original `bar` implementation.
a.bar(1);
// Does not invoke the original `bar` implementation because of the specified `resolver`
// which is passed to `memo`. For any arguments of the function, the resolver will return
// result `1` which will be used as the key.
a.bar(2);

const b = new Qux();
// Does not invoke the method `foo` because there's already an entry
// in the cache which associates the key `1` to the result `42` from the
// invocation of the method `foo` by the instance `a`.
b.foo(1);

// Outputs:
// foo: called
// foo: called
// bar: called

License

MIT