Refactor code to comply with ESLint rules

Major refactoring using ESLint with rules from AirBnb and Vue.

Enable most of the ESLint rules and do necessary linting in the code.
Also add more information for rules that are disabled to describe what
they are and why they are disabled.

Allow logging (`console.log`) in test files, and in development mode
(e.g. when working with `npm run serve`), but disable it when
environment is production (as pre-configured by Vue). Also add flag
(`--mode production`) in `lint:eslint` command so production linting is
executed earlier in lifecycle.

Disable rules that requires a separate work. Such as ESLint rules that
are broken in TypeScript: no-useless-constructor (eslint/eslint#14118)
and no-shadow (eslint/eslint#13014).

tests/integration/application/collections/StatusChecker/FetchFollow.ts

@@ -1,66 +1,100 @@
 import fetch from 'cross-fetch';
 
 export function fetchFollow(
-    url: string, fetchOptions: RequestInit, followOptions: IFollowOptions): Promise<Response> {
-    followOptions = { ...DefaultOptions, ...followOptions };
-    if (!followOptions.followRedirects
-        || followOptions.maximumRedirectFollowDepth === 0) {
-        return fetch(url, fetchOptions);
-    }
-    fetchOptions = { ...fetchOptions, redirect: 'manual' /* handled manually */ };
-    const cookies = new CookieStorage(followOptions.enableCookies);
-    return followRecursivelyWithCookies(
-        url, fetchOptions, followOptions.maximumRedirectFollowDepth, cookies);
+  url: string,
+  fetchOptions: RequestInit,
+  followOptions: IFollowOptions,
+): Promise<Response> {
+  followOptions = { ...DefaultOptions, ...followOptions };
+  if (followRedirects(followOptions)) {
+    return fetch(url, fetchOptions);
+  }
+  fetchOptions = { ...fetchOptions, redirect: 'manual' /* handled manually */ };
+  const cookies = new CookieStorage(followOptions.enableCookies);
+  return followRecursivelyWithCookies(
+    url,
+    fetchOptions,
+    followOptions.maximumRedirectFollowDepth,
+    cookies,
+  );
 }
 
 export interface IFollowOptions {
-    followRedirects?: boolean;
-    maximumRedirectFollowDepth?: number;
-    enableCookies?: boolean;
+  followRedirects?: boolean;
+  maximumRedirectFollowDepth?: number;
+  enableCookies?: boolean;
 }
 
 const DefaultOptions: IFollowOptions = {
-    followRedirects: true,
-    maximumRedirectFollowDepth: 20,
-    enableCookies: true,
+  followRedirects: true,
+  maximumRedirectFollowDepth: 20,
+  enableCookies: true,
 };
 
 async function followRecursivelyWithCookies(
-    url: string, options: RequestInit, followDepth: number, cookies: CookieStorage): Promise<Response> {
-    if (cookies.hasAny()) {
-        options = { ...options, headers: { ...options.headers, cookie: cookies.getHeader() } };
-    }
-    const response = await fetch(url, options);
-    if (!isRedirect(response.status)) {
-        return response;
-    }
-    if (--followDepth < 0) {
-        throw new Error(`[max-redirect] maximum redirect reached at: ${url}`);
-    }
-    const cookieHeader = response.headers.get('set-cookie');
-    cookies.addHeader(cookieHeader);
-    const nextUrl = response.headers.get('location');
-    return followRecursivelyWithCookies(nextUrl, options, followDepth, cookies);
+  url: string,
+  options: RequestInit,
+  followDepth: number,
+  cookies: CookieStorage,
+): Promise<Response> {
+  options = updateCookieHeader(cookies, options);
+  const response = await fetch(url, options);
+  if (!isRedirect(response.status)) {
+    return response;
+  }
+  const newFollowDepth = followDepth - 1;
+  if (newFollowDepth < 0) {
+    throw new Error(`[max-redirect] maximum redirect reached at: ${url}`);
+  }
+  const cookieHeader = response.headers.get('set-cookie');
+  cookies.addHeader(cookieHeader);
+  const nextUrl = response.headers.get('location');
+  return followRecursivelyWithCookies(nextUrl, options, newFollowDepth, cookies);
 }
 
 function isRedirect(code: number): boolean {
-    return code === 301 || code === 302 || code === 303 || code === 307 || code === 308;
+  return code === 301 || code === 302 || code === 303 || code === 307 || code === 308;
 }
 
 class CookieStorage {
-    public cookies = new Array<string>();
-    constructor(private readonly enabled: boolean) {
-    }
-    public hasAny() {
-        return this.enabled && this.cookies.length > 0;
-    }
-    public addHeader(header: string) {
-        if (!this.enabled || !header) {
-            return;
-        }
-        this.cookies.push(header);
-    }
-    public getHeader() {
-        return this.cookies.join(' ; ');
+  public cookies = new Array<string>();
+
+  constructor(private readonly enabled: boolean) {
+  }
+
+  public hasAny() {
+    return this.enabled && this.cookies.length > 0;
+  }
+
+  public addHeader(header: string) {
+    if (!this.enabled || !header) {
+      return;
     }
+    this.cookies.push(header);
+  }
+
+  public getHeader() {
+    return this.cookies.join(' ; ');
+  }
+}
+
+function followRedirects(options: IFollowOptions) {
+  if (!options.followRedirects) {
+    return false;
+  }
+  if (options.maximumRedirectFollowDepth === 0) {
+    return false;
+  }
+  return true;
+}
+
+function updateCookieHeader(
+  cookies: CookieStorage,
+  options: RequestInit,
+): RequestInit {
+  if (!cookies.hasAny()) {
+    return options;
+  }
+  const newOptions = { ...options, headers: { ...options.headers, cookie: cookies.getHeader() } };
+  return newOptions;
 }