I wanted to do a side by side of Immer vs Immutable JS

Immer vs Immutable.js

// Immutable
    import { fromJS } from 'immutable'

    const args = fromJS(nopt(Command.DETAILS.options, Command.DETAILS.shorthands, process.argv, 2))

    const secondArg = args.getIn(['argv', 'remain']).get(1)
    const remote = args.get('remote') || config.default_remote
    const remoteUrl = git.getRemoteUrl(remote)

    const options = args.merge({
        remote,
        number: args.get('number') || secondArg,
        loggedUser: getUser(),
        remoteUser: git.getUserFromRemoteUrl(remoteUrl),
        repo: args.get('repo') || git.getRepoFromRemoteURL(remoteUrl),
        currentBranch: testing ? 'master' : git.getCurrentBranch(),
        github_host: config.github_host,
        github_gist_host: config.github_gist_host,
    })

    let user = args.get('user')
    if (!user) {
        user =
            options.get('repo') || options.get('all')
                ? options.get('loggedUser')
                : process.env.GH_USER || options.get('remoteUser') || options.get('loggedUser')
    }

    function onlyReplaceIfTruthy(oldVal, newVal) {
        return Boolean(newVal) ? newVal : oldVal
    }

    let expandedAliases = {}
    if (config.alias) {
        expandedAliases = {
            fwd: config.alias[options.get('fwd')],
            submit: config.alias[options.get('submit')],
            user: config.alias[user] || user,
        }
    }

    const finalOptions = options.mergeWith(onlyReplaceIfTruthy, { user, ...expandedAliases })
    
 // Immer
    import { produce } from 'immer'

    const args = nopt(Command.DETAILS.options, Command.DETAILS.shorthands, process.argv, 2)

    const options = produce(args, draft => {
        const secondArg = draft.argv.remain[1]
        const remote = draft.remote || config.default_remote
        const remoteUrl = git.getRemoteUrl(remote)

        draft.remote = remote
        draft.number = draft.number || secondArg
        draft.loggedUser = getUser()
        draft.remoteUser = git.getUserFromRemoteUrl(remoteUrl)
        draft.repo = draft.repo || git.getRepoFromRemoteURL(remoteUrl)
        draft.currentBranch = git.getCurrentBranch()
        draft.github_host = config.github_host
        draft.github_gist_host = config.github_gist_host

        if (!draft.user) {
            if (draft.repo || draft.all) {
                draft.user = draft.loggedUser
            } else {
                draft.user = process.env.GH_USER || draft.remoteUser || draft.loggedUser
            }
        }

        if (config.alias) {
            draft.fwd = config.alias[draft.fwd] || draft.fwd
            draft.submit = config.alias[draft.submit] || draft.submit
            draft.user = config.alias[draft.user] || draft.user
        }
    })