JavaScript Dependency Injection

Question

I am new at JavaScript. I wonder how dependency injection is being implemented in JavaScript? I searched the internet but couldn\'t find anything.

Answer 1

I'd say DI is an out-of-the-box feature of JS/ES2015. :-) Of course, it is not full featured IOC containers but looks useful, doesn't it? Check out an example below!

const one = () => 1;
const two = ({one}) => one + one;
const three = ({one, two}) => one + two;

// IOC container
const decimalNumbers = {
  get one() { return one(this); },
  get two() { return two(this); },
  get three() { return three(this); }
};

const binaryTwo = ({one}) => one + 9;

// child IOC container
const binaryNumbers = Object.create(decimalNumbers, {
  two: { get() { return binaryTwo(this); } }
});

console.log(`${decimalNumbers.three} is ${binaryNumbers.three} in binary`);

You can wrap dependencies in _.once (see underscore or lodash) to turn them into singletons.

const rand = function() {
  return (min, max) => min + Math.random() * (max - min) | 0;
};

const pair = function({rand} = this) {
  return [rand(10, 100), rand(100, 1000)];
};

// IOC container
const ioc = Object.create({}, {
  rand: {get: rand},
  pair: {get: _.once(pair)} // singleton
});

console.log(`${[ioc.pair, ioc.pair === ioc.pair]}`);