discord.js/src/rest/RESTManager.js

const UserAgentManager = require('./UserAgentManager');
const handlers = require('./handlers');
const APIRequest = require('./APIRequest');
const routeBuilder = require('./APIRouter');
const { Error } = require('../errors');
const { Endpoints, browser } = require('../util/Constants');

class RESTManager {
  constructor(client, tokenPrefix = 'Bot') {
    this.client = client;
    this.handlers = {};
    if (!browser) this.userAgentManager = new UserAgentManager(this);
    this.rateLimitedEndpoints = {};
    this.globallyRateLimited = false;
    this.tokenPrefix = tokenPrefix;
    this.versioned = true;
  }

  get api() {
    return routeBuilder(this);
  }

  getAuth() {
    const token = this.client.token || this.client.accessToken;
    const prefixed = !!this.client.application || (this.client.user && this.client.user.bot);
    if (token && prefixed) return `${this.tokenPrefix} ${token}`;
    else if (token) return token;
    throw new Error('TOKEN_MISSING');
  }

  get cdn() {
    return Endpoints.CDN(this.client.options.http.cdn);
  }

  destroy() {
    for (const handler of Object.values(this.handlers)) {
      if (handler.destroy) handler.destroy();
    }
  }

  push(handler, apiRequest) {
    return new Promise((resolve, reject) => {
      handler.push({
        request: apiRequest,
        resolve,
        reject,
      });
    });
  }

  getRequestHandler() {
    const method = this.client.options.apiRequestMethod;
    if (typeof method === 'function') return method;
    const handler = handlers[method];
    if (!handler) throw new Error('RATELIMIT_INVALID_METHOD');
    return handler;
  }

  request(method, url, options = {}) {
    const apiRequest = new APIRequest(this, method, url, options);
    if (!this.handlers[apiRequest.route]) {
      this.handlers[apiRequest.route] = new handlers.RequestHandler(this, this.getRequestHandler());
    }

    return this.push(this.handlers[apiRequest.route], apiRequest);
  }

  set endpoint(endpoint) {
    this.client.options.http.api = endpoint;
  }
}

module.exports = RESTManager;