MemoizeObject is a decorator which memoize methods using their value checksum as a cache key instead of reference ID.

memoize-object-decorator

A decorator returns memoized method which compares objects and arrays by value.

Installation

npm i memoize-object-decorator

Usage

``typescript
import { MemoizeObject } from 'memoize-object-decorator';

interface Person {
name: string;
age: number;
}

class SomeClass {
@MemoizeObject()
factorial(num: number): number {
return (num <= 1) ? 1 : num * this.factorial(--num);
}

@MemoizeObject() // for circular structures @MemoizeObject({circular: true})
getFactorialOfPersonAgeMinusSomething(obj: Person, somethingToSubtract: number): number {
return this.factorial(obj.age) - somethingToSubtract;
}
}

const fact: SomeClass = new SomeClass();
const person: Person = {
name: "John Doe",
age: 10
}

fact.factorial(10); // 3628800
fact.factorial(10); // 3628800, cache hitted 1 time for factorial(10) and returned 3628800
fact.factorial(15); // 1307674368000, cache hitted 1 time for factorial(10) and returned 3628800

fact.getFactorialOfPersonAgeMinusSomething(person, 10) // 3628790, cache hitted 1 time for factorial(10) and returned 3628800
fact.getFactorialOfPersonAgeMinusSomething(person, 10) // 3628790, cache for fact.getFactorialOfPersonAgeMinusSomething hitted 1 time

person.age = 12;

fact.getFactorialOfPersonAgeMinusSomething(person, 10) // 479001590, cache hitted 1 time for factorial(12) and returned 479001600
fact.getFactorialOfPersonAgeMinusSomething(person, 10) // 479001590, cache for fact.getFactorialOfPersonAgeMinusSomething hitted 1 time
fact.getFactorialOfPersonAgeMinusSomething(person, 20) // 479001580, cache hitted 1 time for factorial(12) and returned 479001600
`

Comparision with standard lodash memoize function/decorator

`typescript
import { Memoize } from 'lodash-decorators';

interface Person {
name: string;
age: number;
}

class SomeClass {
@Memoize()
factorial(num: number): number {
return (num <= 1) ? 1 : num * this.factorial(--num);
}

@Memoize()
getFactorialOfPersonAgeMinusSomething(obj: Person, somethingToSubtract: number): number {
return this.factorial(obj.age) - somethingToSubtract;
}
}

const fact: SomeClass = new SomeClass();
const person: Person = {
name: "John Doe",
age: 10
}

fact.factorial(10); // 3628800
fact.factorial(10); // 3628800, cache hitted 1 time for factorial(10) and returned 3628800
fact.factorial(15); // 1307674368000, cache hitted 1 time for factorial(10) and returned 3628800

fact.getFactorialOfPersonAgeMinusSomething(person, 10) // 3628790, cache hitted 1 time for factorial(10) and returned 3628800
fact.getFactorialOfPersonAgeMinusSomething(person, 10) // 3628790, cache for fact.getFactorialOfPersonAgeMinusSomething hitted 1 time

person.age = 12;

fact.getFactorialOfPersonAgeMinusSomething(person, 10) // 3628790, cache for fact.getFactorialOfPersonAgeMinusSomething hitted 1 time
fact.getFactorialOfPersonAgeMinusSomething(person, 10) // 3628790, cache for fact.getFactorialOfPersonAgeMinusSomething hitted 1 time
fact.getFactorialOfPersonAgeMinusSomething(person, 20) // 3628790, cache for fact.getFactorialOfPersonAgeMinusSomething hitted 1 time
``

What's going on under the hood?

The decorator takes all of the arguments of memoized method and calculates their unique SHA1 hash which is used as a Map key for cache.

In this way we can track objects and arrays by their values instead of the reference.

Important

SHA1 hash calculation process is slow in general, so it is not recommended to use this decorator for methods which takes huge objects or/and arrays as an arguments.