Migrate platform to use a "real" host interface style.

lib/backburner/host-platform.ts

@@ -0,0 +1,53 @@
+export interface IPlatform {
+  setTimeout(fn: () => void, ms: number): any;
+  clearTimeout(id: any): void;
+  next(): any;
+  clearNext(timerId: any): void;
+  now(): number;
+}
+
+const SET_TIMEOUT = setTimeout;
+const NOOP = () => {};
+
+export function buildDefaultPlatform(flush: () => void): IPlatform {
+  let next;
+  let clearNext = NOOP;
+
+  if (typeof Promise === 'function') {
+    const autorunPromise = Promise.resolve();
+    next = () => autorunPromise.then(flush);
+
+    // supports IE11
+  } else if (typeof MutationObserver === 'function') {
+    let iterations = 0;
+    let observer = new MutationObserver(flush);
+    let node = document.createTextNode('');
+    observer.observe(node, { characterData: true });
+
+    next = () => {
+      iterations = ++iterations % 2;
+      node.data = '' + iterations;
+      return iterations;
+    };
+
+  } else {
+    next = () => SET_TIMEOUT(flush, 0);
+  }
+
+  return {
+    setTimeout(fn, ms) {
+      return SET_TIMEOUT(fn, ms);
+    },
+
+    clearTimeout(timerId: number) {
+      return clearTimeout(timerId);
+    },
+
+    now() {
+      return Date.now();
+    },
+
+    next,
+    clearNext,
+  };
+}

lib/index.ts

@@ -1,3 +1,12 @@
+export {
+  buildDefaultPlatform,
+  IPlatform
+} from './backburner/host-platform';
+
+import {
+  buildDefaultPlatform,
+  IPlatform,
+} from './backburner/host-platform';
 import {
   findItem,
   findTimer,
@@ -16,7 +25,6 @@ import Queue, { QUEUE_STATE } from './backburner/queue';
 type Timer = any;
 
 const noop = function() {};
-const SET_TIMEOUT = setTimeout;
 
 function parseArgs() {
   let length = arguments.length;
@@ -45,14 +53,22 @@ function parseArgs() {
   return [target, method, args];
 }
 
+export interface IBackburnerOptions {
+  defaultQueue?: string;
+  onBegin?: (currentInstance: DeferredActionQueues, previousInstance: DeferredActionQueues) => void;
+  onEnd?: (currentInstance: DeferredActionQueues, nextInstance: DeferredActionQueues) => void;
+  mustYield?: () => boolean;
+  _buildPlatform: (flush: () => void) => IPlatform;
+}
+
 export default class Backburner {
   public static Queue = Queue;
 
   public DEBUG = false;
 
   public currentInstance: DeferredActionQueues | null = null;
 
-  public options: any;
+  public options: IBackburnerOptions;
 
   private _onBegin: Function;
   private _onEnd: Function;
@@ -67,22 +83,16 @@ export default class Backburner {
 
   private _timerTimeoutId: number | null = null;
   private _timers: any[];
-  private _platform: {
-    setTimeout(fn: () => void, ms: number): number;
-    clearTimeout(id: number): void;
-    next(fn: () => void): number;
-    clearNext(fn): void;
-    now(): number;
-  };
+  private _platform: IPlatform;
 
   private _boundRunExpiredTimers: () => void;
 
   private _autorun: number | null = null;
   private _boundAutorunEnd: () => void;
 
-  constructor(queueNames: string[], options: any = {} ) {
+  constructor(queueNames: string[], options: IBackburnerOptions) {
     this.queueNames = queueNames;
-    this.options = options;
+    this.options = options || {};
     if (!this.options.defaultQueue) {
       this.options.defaultQueue = queueNames[0];
     }
@@ -111,41 +121,8 @@ export default class Backburner {
       this.end(true /* fromAutorun */);
     };
 
-    let _platform = this.options._platform || {};
-    let platform = Object.create(null);
-    platform.setTimeout = _platform.setTimeout || ((fn, ms) => setTimeout(fn, ms));
-    platform.clearTimeout = _platform.clearTimeout || ((id) => clearTimeout(id));
-    platform.clearNext = _platform.clearNext || platform.clearTimeout;
-    platform.now = _platform.now || (() => Date.now());
-
-    // TODO: do we need this?
-    if (_platform.next) {
-      platform.next = _platform.next;
-
-    // supports Node and "evergreen" browsers
-    } else if (typeof Promise === 'function') {
-      const autorunPromise = Promise.resolve();
-      platform.next = () => autorunPromise.then(this._boundAutorunEnd);
-
-    // supports IE11
-    } else if (typeof MutationObserver === 'function') {
-      let iterations = 0;
-      let observer = new MutationObserver(this._boundAutorunEnd);
-      let node = document.createTextNode('');
-      observer.observe(node, { characterData: true });
-
-      platform.next = () => {
-        iterations = ++iterations % 2;
-        node.data = '' + iterations;
-        return iterations;
-      };
-
-    // do we need this fallback?
-    } else {
-      platform.next = () => SET_TIMEOUT(this._boundAutorunEnd, 0);
-    }
-
-    this._platform = platform;
+    let builder = this.options._buildPlatform || buildDefaultPlatform;
+    this._platform = builder(this._boundAutorunEnd);
   }
 
   /*
@@ -797,6 +774,6 @@ export default class Backburner {
 
   private _scheduleAutorun() {
     const next = this._platform.next;
-    this._autorun = next(this._boundAutorunEnd);
+    this._autorun = next();
   }
 }