memoizer-ts v1.0.1

memoizer-ts

The Memoizer adds memoization to arbitrary functions. The original function will only be called once for identical sets of arguments, subsequent calls will be returned with memoized results.

For more complex signatures, this Memoizer allows to define custom Equality-Comparers for comparing parameters.

Getting started

Install the package

npm install memoizer-ts --save

Use the Memoizer

The Memoizer can be used to add memoization to any function. It makes use of TypeScript's type system to return a strongly typed new function with the same signature as your original function.

import {Memoizer} from 'memoizer-ts';

class MyClass {
  public calculate = Memoizer.makeMemoized(this.calculateImplementation);

  private calculateImplementation(n: number): number { ... }
}

Recursive example

You can also define a recursive function that calls the memoized version of itself. This can be especially useful if the recursion leads to multiple calls to the function with the same set of parameters. This example calculates the n-th Fibonacci number, making use of memoization and thus avoiding repetitive calculations for the same n.

const nthFibonacci = Memoizer.makeMemoized(n =>
  n === 0 || n === 1 ? n :
  nthFibonacci(n-1) + nthFibonacci(n-2));

Note: This example results in rounding errors rather quickly, it is just for demonstration purposes to show how memoization can speed up a recursive function significantly (although of course there are other, faster ways for the Fibonacci-sequence).

Equality Comparers

By default, parameters of memoized function calls will be compared by strict equality (===). You can provide custom equality comparers to the Memoizer, in the same order as the parameters that should be compared. You can skip individual equality comparers by passing null; in the following (totally made up) example we provide an equality comparer for the second parameter:

// We know that the underlying function will behave the same for
// all even values and all odd values. So we provide such an EqualityComparer:
const memoized = Memoizer.makeMemoized(fn, null, {
    getHashCode: (x) => x % 2,
    equals: (a, b) => a % 2 === b % 2
});