1"use strict"; 2 3// rawAsap provides everything we need except exception management. 4var rawAsap = require("./raw"); 5// RawTasks are recycled to reduce GC churn. 6var freeTasks = []; 7// We queue errors to ensure they are thrown in right order (FIFO). 8// Array-as-queue is good enough here, since we are just dealing with exceptions. 9var pendingErrors = []; 10var requestErrorThrow = rawAsap.makeRequestCallFromTimer(throwFirstError); 11 12function throwFirstError() { 13 if (pendingErrors.length) { 14 throw pendingErrors.shift(); 15 } 16} 17 18/** 19 * Calls a task as soon as possible after returning, in its own event, with priority 20 * over other events like animation, reflow, and repaint. An error thrown from an 21 * event will not interrupt, nor even substantially slow down the processing of 22 * other events, but will be rather postponed to a lower priority event. 23 * @param {{call}} task A callable object, typically a function that takes no 24 * arguments. 25 */ 26module.exports = asap; 27function asap(task) { 28 var rawTask; 29 if (freeTasks.length) { 30 rawTask = freeTasks.pop(); 31 } else { 32 rawTask = new RawTask(); 33 } 34 rawTask.task = task; 35 rawAsap(rawTask); 36} 37 38// We wrap tasks with recyclable task objects. A task object implements 39// `call`, just like a function. 40function RawTask() { 41 this.task = null; 42} 43 44// The sole purpose of wrapping the task is to catch the exception and recycle 45// the task object after its single use. 46RawTask.prototype.call = function () { 47 try { 48 this.task.call(); 49 } catch (error) { 50 if (asap.onerror) { 51 // This hook exists purely for testing purposes. 52 // Its name will be periodically randomized to break any code that 53 // depends on its existence. 54 asap.onerror(error); 55 } else { 56 // In a web browser, exceptions are not fatal. However, to avoid 57 // slowing down the queue of pending tasks, we rethrow the error in a 58 // lower priority turn. 59 pendingErrors.push(error); 60 requestErrorThrow(); 61 } 62 } finally { 63 this.task = null; 64 freeTasks[freeTasks.length] = this; 65 } 66}; 67