I FUCK DOGS

'use strict'

const Promise = require('es6-promise').Promise;
const PixivAppApi = require('pixiv-app-api')
/* PixivAppApi.prototype.
constructor(username?: string, password?: string): PixivAppApi
login(username?: string, password?: string): Promise
userDetail(id: ID, params?: Object): Promise
    params = { restrict='public', offset=0 }
userFollowing(id: ID, params?: Object): Promise
*/

// =============================================================================

function initPixiv( authInfo ) {
    const pixiv = new PixivAppApi()
    if (authInfo) {
        return pixiv.login(authInfo.username, authInfo.password).then(() => {
            return { pixiv }
        })
    } else {
        return Promise.resolve({ pixiv })
    }
}

function getFollowingUsers( {pixiv, userID} ) {
    return pixiv.userDetail(userID).then((res) => {
        const pagesCount = Math.ceil(res.profile.totalFollowUsers / 30)
        const pagesOffsets = Array(pagesCount).fill(0).map((x,i) => i*30)
        return Promise.all(
            pagesOffsets.map( (x) => pixiv.userFollowing(userID, {offset: x}) )
        ).then( responses => {
            const nestedUsers = responses.map((page) =>
                page.userPreviews.map((prev) => { return {
                    id: prev.user.id,
                    name: prev.user.id,
                    account: prev.user.account,
                    avatarURL: prev.user.profileImageUrls.medium
                } })
            )
            const flattedUsers = [].concat.apply([], nestedUsers)
            return { pixiv, following: flattedUsers }
        })
    })
}

// =============================================================================

const MY_AUTH_INFO = undefined // можно не логинится
const SOME_ID = 393516

initPixiv( MY_AUTH_INFO )
    .then(res => getFollowingUsers({ pixiv: res.pixiv, userID: SOME_ID }))
    .then(res => console.log(res.following))
    .catch(err => console.log(err))