Lazy is a TypeScript/JavaScript library that makes it easy to work with lazy values. This is particularly useful for optimizing performance by deferring expensive computations until their results are needed, and only computing them once. Lazy provides both functional and object-oriented APIs—both of which have been tested extensively—so that you can integrate it into your project easily.

Features

• Deferred Computations: Create and manage deferred computations.
• Value Caching: Cache the results of computations to avoid redundant executions.
• Flexible Mapping: Map functions over lazy values to transform their results.
• Functional and Object-Oriented APIs: Use your preference between the functional API or the object-oriented API to work with lazy values.

Installation

Install the library using your preferred package manager:

# bun
bunx jsr add @trav/lazy

# npm
npx jsr add @trav/lazy

# deno
deno add @trav/lazy

# pnpm
pnpm dlx jsr add @trav/lazy

#yarn
yarn dlx jsr add @trav/lazy

Usage

Functional API (default)

Creating a Lazy Value

import { Lazy } from "@trav/lazy";

const x = Lazy(() => {
    // some expensive computation
    // this will only execute once
    return 69;
});

Forcing a Lazy Value

const result = Lazy.force(x);
console.log(result); // 69

Mapping a Function Over a Lazy Value

const mappedValue = Lazy.map((v) => v * 2, x);
const result = Lazy.force(mappedValue);
console.log(result); // 138

You can also use Lazy.mapVal to map a function over a lazy value, which can be more efficient if x is already forced.

const mappedValue = Lazy.mapVal((v) => v * 2, x);
const result = Lazy.force(mappedValue);
console.log(result); // 138

Check if a Lazy value has already been forced

const hasBeenForced = Lazy.isValue(x);
console.log(hasBeenForced); // true

Create a Lazy value from a regular value

const lazyFromValue = Lazy.fromValue(69);
const hasBeenForced = Lazy.isValue(lazyFromValue);
console.log(hasBeenForced); // true

Object-Oriented API

Creating a Lazy Instance

import { Lazy } from "@trav/lazy/oop";

const x = new Lazy(() => {
    // some expensive computation
    return 69;
});

Forcing a Lazy Instance

const result = x.force();
console.log(result); // 69

Mapping a Function Over a Lazy Instance

const mappedInstance = x.map((x: number) => x * 2);
const result = mappedInstance.force();
console.log(result); // 138

You can also use Lazy.prototype.mapVal to map a function over a lazy value, which can be more efficient if the current instance is already forced.

const mappedInstance = x.mapVal((v) => v * 2);
const result = mappedInstance.force();
console.log(result); // 138

Create a Lazy Instance from a regular value

const lazyFromValue = Lazy.fromVal(69);
const hasBeenForced = Lazy.isValue(lazyFromValue);
console.log(hasBeenForced); // true

Handling Exceptions

If a function throws an error, the same error is thrown when forcing the lazy value. This is the same in both the functional and object-oriented APIs.

const faulty = Lazy(() => {
    throw new Error("Something went wrong");
});

try {
    Lazy.force(faulty);
} catch (e) {
    console.error(e); // Error: Something went wrong
}

Contributing

Contributions are welcome! Please open an issue or submit a pull request.

License

This project is licensed under the MIT License. See the LICENSE file for details.

Contact

For any questions or suggestions, please open an issue, or reach out to me on Twitter.

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Feel free to explore the source code and improve upon it.