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idd

A dependency injection system with destructuring. Combines a common pattern of using a single destructuring argument to avoid confusing the order of arguments to high-parity functions, possibly with many optional parameters.

Getting Started

To install the dependency injection system, use npm install

npm install --save idd

Then, from other peer directories, you can require the files as properties on the directory's default export

lib/config.js

export default function () {
    return {
        language: 'ru-ru',
        level: 'info'
    };
};

lib/greeter.js

export default ({config, Logger}) => {
    const logger = new Logger();
    return {
        greet: () => {
            if (config.language === 'en-us') {
                logger.log('Hello World!');
            } else if (config.language === 'ru-ru') {
                logger.log('Привет, мир!');
            } else {
                logger.error('unsupported language ' + config.language);
            }
        }
    };
};

lib/Logger.js

import chalk from 'chalk';
 
export default () => class Logger {
    constructor() {
        this.level = process.env.LEVEL;
    }
    log(msg) {
        if (this.level !== 'quiet') {
            console.log(msg);
        }
    }
    error(msg) {
        if (this.level !== 'quiet' && this.level !== 'silent') {
            chalk.red(msg);
        }
    }
};

index.js

import path from 'path';
import idd from '../../../..';
 
const {greeter} = idd(path.join(__dirname, 'lib'));
 
greeter.greet();

Then the output would be 'Hello World!'. If you were to change config to be instead

export default function() {
    language: 'ru-ru',
    level: 'error'
}

Then the output would be 'Привет, мир!'.

Testing

A good dependency injection system should make unit testing easy. To mock out your dependencies, just provide an optional third option with the mocks

import {sinon} from 'sinon';
import idd from 'idd';
import test from 'ava';
 
test('Greet was called', t => {
    const greet = sinon.spy();
    const config = { greeting: 'Hello World!'};
    const {greeter} = idd('./lib', { config, greet });
 
    greeter.greet();
 
    t.true(greet.calledOnce);
});