typescript-memoize

What is typescript-memoize?

The `typescript-memoize` package provides decorators for memoizing methods in TypeScript. Memoization is a technique used to speed up function calls by caching the results of expensive function calls and returning the cached result when the same inputs occur again.

What are typescript-memoize's main functionalities?

Basic Memoization

This feature allows you to memoize a method so that the result is cached based on the input parameters. The second call with the same input will return the cached result without recomputing.

class Example {
  @Memoize()
  computeExpensiveValue(input: number): number {
    console.log('Computing...');
    return input * 2; // Simulate an expensive computation
  }
}

const example = new Example();
console.log(example.computeExpensiveValue(5)); // Computing... 10
console.log(example.computeExpensiveValue(5)); // 10 (cached result)

Custom Cache Key

This feature allows you to specify a custom cache key for the memoization. This can be useful if you need more control over how the cache keys are generated.

class Example {
  @Memoize((input: number) => `key-${input}`)
  computeExpensiveValue(input: number): number {
    console.log('Computing...');
    return input * 2; // Simulate an expensive computation
  }
}

const example = new Example();
console.log(example.computeExpensiveValue(5)); // Computing... 10
console.log(example.computeExpensiveValue(5)); // 10 (cached result)

Expiration Time

This feature allows you to set a time-to-live (TTL) for the cached result. After the TTL expires, the cached result will be invalidated, and the method will be recomputed.

class Example {
  @Memoize({ ttl: 5000 })
  computeExpensiveValue(input: number): number {
    console.log('Computing...');
    return input * 2; // Simulate an expensive computation
  }
}

const example = new Example();
console.log(example.computeExpensiveValue(5)); // Computing... 10
setTimeout(() => {
  console.log(example.computeExpensiveValue(5)); // Computing... 10 (cache expired)
}, 6000);

Other packages similar to typescript-memoize

lodash

Lodash is a popular utility library that provides a wide range of functions, including memoization. The `_.memoize` function in Lodash can be used to memoize functions, but it does not provide decorators out of the box. Lodash is more general-purpose and includes many other utilities beyond memoization.

memoizee

Memoizee is a dedicated memoization library for JavaScript. It offers a rich set of features for memoizing functions, including support for custom cache keys, expiration times, and more. Unlike `typescript-memoize`, it does not provide decorators specifically for TypeScript.

moize

Moize is another memoization library that offers a wide range of configuration options, including custom cache keys, expiration times, and more. It is designed to be highly configurable and performant. Like `memoizee`, it does not provide TypeScript decorators but can be used in TypeScript projects.

README

typescript-memoize

A memoize decorator for Typescript.

Installation

npm install --save typescript-memoize

Usage:

@Memoize(hashFunction?: (...args: any[]) => any)

You can use it in four ways:

• Memoize a get accessor,
• Memoize a method which takes no parameters,
• Memoize a method which varies based on its first parameter only,
• Memoize a method which varies based on some combination of parameters

You can call memoized methods within the same class, too. This could be useful if you want to memoize the return value for an entire data set, and also a filtered or mapped version of that same set.

Memoize a get accessor, or a method which takes no parameters

These both work the same way. Subsequent calls to a memoized method without parameters, or to a get accessor, always return the same value.

I generally consider it an anti-pattern for a call to a get accessor to trigger an expensive operation. Simply adding Memoize() to a get allows for seamless lazy-loading.

import {Memoize} from 'typescript-memoize';

class SimpleFoo {

	// Memoize a method without parameters
	@Memoize()
	public getAllTheData() {
		// do some expensive operation to get data
		return data;
	}

	// Memoize a getter
	@Memoize()
	public get someValue() {
		// do some expensive operation to calculate value
		return value;
	}

}

And then we call them from somewhere else in our code:

let simpleFoo = new SimpleFoo();

// Memoizes a calculated value and returns it:
let methodVal1 = simpleFoo.getAllTheData();

// Returns memoized value
let methodVal2 = simpleFoo.getAllTheData();

// Memoizes (lazy-loads) a calculated value and returns it:
let getterVal1 = simpleFoo.someValue;

// Returns memoized value
let getterVal2 = simpleFoo.someValue;

Memoize a method which varies based on its first parameter only

Subsequent calls to this style of memoized method will always return the same value.

I'm not really sure why anyone would use this approach to memoize a method with more than one parameter, but it's possible.

import {Memoize} from 'typescript-memoize';

class ComplicatedFoo {

	// Memoize a method without parameters (just like the first example)
	@Memoize()
	public getAllTheData() {
		// do some expensive operation to get data
		return data;
	}

	// Memoize a method with one parameter
	@Memoize()
	public getSomeOfTheData(id: number) {
		let allTheData = this.getAllTheData(); // if you want to!
		// do some expensive operation to get data
		return data;
	}

	// Memoize a method with multiple parameters
	// Only the first parameter will be used for memoization
	@Memoize()
	public getGreeting(name: string, planet: string) {
		return 'Hello, ' + name + '! Welcome to ' + planet;
	}

}

We call these methods from somewhere else in our code:

let complicatedFoo = new ComplicatedFoo();

// Returns calculated value and memoizes it:
let oneParam1 = complicatedFoo.getSomeOfTheData();

// Returns memoized value
let oneParam2 = complicatedFoo.getSomeOfTheData();

// Memoizes a calculated value and returns it:
// 'Hello, Darryl! Welcome to Earth'
let greeterVal1 = complicatedFoo.getGreeting('Darryl', 'Earth');

// Ignores the second parameter, and returns memoized value
// 'Hello, Darryl! Welcome to Earth'
let greeterVal2 = complicatedFoo.getGreeting('Darryl', 'Mars');

Memoize a method which varies based on some combination of parameters

Pass in a hashFunction which takes the same parameters as your target method, to memoize values based on all parameters, or some other custom logic

import {Memoize} from 'typescript-memoize';

class MoreComplicatedFoo {

	// Memoize a method with multiple parameters
	// Memoize will remember values based on keys like: 'name;planet'
	@Memoize((name: string, planet: string) => {
		return name + ';' + string;
	})
	public getBetterGreeting(name: string, planet: string) {
		return 'Hello, ' + name + '! Welcome to ' + planet;
	}
	
	// Memoize based on some other logic
	@Memoize(() => {
		return new Date();
	})
	public memoryLeak(greeting: string) {
		return greeting + '!!!!!';
	}

}

We call these methods from somewhere else in our code. By now you should be getting the idea:

let moreComplicatedFoo = new MoreComplicatedFoo();

// 'Hello, Darryl! Welcome to Earth'
let greeterVal1 = moreComplicatedFoo.getBetterGreeting('Darryl', 'Earth');

// 'Hello, Darryl! Welcome to Mars'
let greeeterVal2 = moreComplicatedFoo.getBetterGreeting('Darryl', 'Mars');

// Fill up the computer with useless greetings:
let greeting = moreComplicatedFoo.memoryLeak('Hello');