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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
/* eslint-env amd */
"use strict";
/* global workerHelper */
/* exported workerHelper */
(function (root, factory) {
if (typeof define === "function" && define.amd) {
define(factory);
} else if (typeof exports === "object") {
module.exports = factory();
} else {
root.workerHelper = factory();
}
})(this, function () {
/**
* This file is to only be included by ChromeWorkers. This exposes
* a `createTask` function to workers to register tasks for communication
* back to `devtools/shared/worker`.
*
* Tasks can be send their responses via a return value, either a primitive
* or a promise.
*
* createTask(self, "average", function (data) {
* return data.reduce((sum, val) => sum + val, 0) / data.length;
* });
*
* createTask(self, "average", function (data) {
* return new Promise((resolve, reject) => {
* resolve(data.reduce((sum, val) => sum + val, 0) / data.length);
* });
* });
*
*
* Errors:
*
* Returning an Error value, or if the returned promise is rejected, this
* propagates to the DevToolsWorker as a rejected promise. If an error is
* thrown in a synchronous function, that error is also propagated.
*/
/**
* Takes a worker's `self` object, a task name, and a function to
* be called when that task is called. The task is called with the
* passed in data as the first argument
*
* @param {object} self
* @param {string} name
* @param {function} fn
*/
function createTask(self, name, fn) {
// Store a hash of task name to function on the Worker
if (!self._tasks) {
self._tasks = {};
}
// Create the onmessage handler if not yet created.
if (!self.onmessage) {
self.onmessage = createHandler(self);
}
// Store the task on the worker.
self._tasks[name] = fn;
}
/**
* Creates the `self.onmessage` handler for a Worker.
*
* @param {object} self
* @return {function}
*/
function createHandler(self) {
return function (e) {
const { id, task, data } = e.data;
const taskFn = self._tasks[task];
if (!taskFn) {
self.postMessage({ id, error: `Task "${task}" not found in worker.` });
return;
}
try {
handleResponse(taskFn(data));
} catch (ex) {
handleError(ex);
}
function handleResponse(response) {
// If a promise
if (response && typeof response.then === "function") {
response.then(
val => self.postMessage({ id, response: val }),
handleError
);
} else if (response instanceof Error) {
// If an error object
handleError(response);
} else {
// If anything else
self.postMessage({ id, response });
}
}
function handleError(error = "Error") {
try {
// First, try and structured clone the error across directly.
self.postMessage({ id, error });
} catch (x) {
// We could not clone whatever error value was given. Do our best to
// stringify it.
let errorString = `Error while performing task "${task}": `;
try {
errorString += error.toString();
} catch (ex) {
errorString += "<could not stringify error>";
}
if ("stack" in error) {
try {
errorString += "\n" + error.stack;
} catch (err) {
// Do nothing
}
}
self.postMessage({ id, error: errorString });
}
}
};
}
return { createTask };
});