Abstract dictionaries in ES2015 with immutability and method chaining

dict-symbol.js

const repository = Symbol('repository')

class Dict {
    constructor(props) {
        if (typeof props !== 'object') {
            throw new Error(
                `Props must be an object, you passed ${typeof props} ${props}.`
            )
        }
        Object.freeze(props)
        Object.defineProperty(this, repository, {
            value: props,
        })
        Object.freeze(this)
    }

    merge(props) {
        return new Dict({
            ...this[repository],
            ...props,
        })
    }

    set(key, value) {
        return new Dict({
            ...this[repository],
            [key]: value,
        })
    }

    get(key) {
        return this[repository][key]
    }
}

module.exports = Dict

dict-weakmap.js

const weakMap = new WeakMap()

class Dict {
    constructor(props) {
        if (typeof props !== 'object') {
            throw new Error(
                `Props must be an object, you passed ${typeof props} ${props}.`
            )
        }
        weakMap.set(this, props)
        Object.freeze(this)
    }

    set(key, value) {
        return new Dict({
            ...weakMap.get(this),
            [key]: value,
        })
    }

    merge(props) {
        return new Dict({
            ...weakMap.get(this),
            ...props,
        })
    }

    get(key) {
        return weakMap.get(this)[key]
    }
}

module.exports = Dict