options-defaults

Options-defaults design pattern implementation for reliable configuration. It merges objects deeply, overrides arrays and classes (different than Object) and the result remains strongly typed.

Table of contents

1. Getting Started

2. Usage

3. Features

Getting Started

npm i options-defaults

Usage

Design pattern - OOP way

import { defaults } from 'options-defaults';

export interface SomeOptions {
    logger?: Partial<Console>;
}

export class Something {
    static defaults = {
        logger: console,
    };

    options: SomeOptions & typeof Something.defaults;
    constructor(options?: SomeOptions) {
        this.options = defaults(Something.defaults, options);
    }
}

Design pattern - Functional way

import { defaults } from 'options-defaults';

export interface SomeOptions {
    logger?: Partial<Console>;
}

const somethingDefaults = {
    logger: console,
};

export const doSomething = (options: SomeOptions) => {
    const config = defaults(somethingDefaults, options);
};

Behavior

import { defaults } from 'options-defaults';

class TestLogger {
    constructor(public name = `TestLogger`) {}

    log() {
        console.log(`Call from ${this.name}`);
    }
}

const someDefaults = {
    console,
    nested: {
        property: 'default',
        shouldBeDefault: 'default',
        array: ['default1', 'default2'],
    },
};

const someOptions = {
    nested: {
        property: 'overriden',
        array: ['overriden1'],
    },
    array: ['overriden'],
};

const options = defaults(
    someDefaults,
    someOptions,
    {
        console: {
            log: () => {
                console.log(`TEST`);
            },
        },
    },
    {
        console: new TestLogger(),
    },
);

options.console.log(`log`); // "Call from TestLogger"
options.console.debug(`debug`); // "debug"

// options will be:
{
    "nested": {
        "property": "overriden",
        "shouldBeDefault": "default",
        "array": [
            "overriden1"
        ]
    },
    "array": [
        "overriden"
    ]
}

// someDefaults will not be mutated!

Features

• Beats alternatives - better alternative to {...defaults, ...options} destructing and lodash _.defaults or _.merge
• Secure - immune to prototype pollution attack
• Simple - just 40 lines of clean TypeScript code
• Strongly typed - result remains strongly typed