node-unhandled-rejection/src/index.js

'use strict';

const debug = require("debug")("unhandled-rejection");
const EventEmitter = require("events").EventEmitter;
const rejectionStore = require("./rejection-store");

let unhandledTimeout = 60 * 1000;
let unhandledPromises = [];

module.exports = function(options = {}) {
	let emitter = new EventEmitter();
	let store = rejectionStore(options.timeout);

	function extractPromiseRejectionEvent(event) {
		let errorData = {};

		if (event.detail != null && event.detail.reason != null) {
			errorData.error = event.detail.reason;
		} else if (event.reason != null) {
			errorData.error = event.reason;
		}

		if (event.detail != null && event.detail.promise != null) {
			errorData.promise = event.detail.promise;
		} else if (event.promise != null) {
			errorData.promise = event.promise;
		}

		return errorData;
	}

	function handleEvent(event, errorData) {
		if (event != null && event.preventDefault != null && typeof event.preventDefault === "function") {
			event.preventDefault();
		}

		if (errorData == null) {
			if (event != null) {
				errorData = extractPromiseRejectionEvent(event);
			}
		}

		return errorData;
	}

	function deduplicateError(errorData) {
		/* This is to deal with the case where an unhandled rejection comes in through
		 * more than one event interface, eg. in browser code. It returns a boolean
		 * indicating whether to continue the emitting process.
		 */
		return (!store.exists(errorData));
	}

	function handleUnhandledRejection(event, errorData) {
		debug("Got unhandledRejection");

		let normalizedErrorData = handleEvent(event, errorData);

		if (deduplicateError(normalizedErrorData)) {
			store.register(normalizedErrorData);

			debug("Emitting unhandledRejection...");
			emitter.emit("unhandledRejection", normalizedErrorData.error, normalizedErrorData.promise);
		} else {
			debug("Ignoring unhandledRejection as duplicate");
		}
	}

	function handleRejectionHandled(event, errorData) {
		debug("Got rejectionHandled");
		let normalizedErrorData = handleEvent(event, errorData);
		store.unregister(normalizedErrorData)

		debug("Emitting rejectionHandled...");
		emitter.emit("rejectionHandled", normalizedErrorData.error, normalizedErrorData.promise);
	}

	function onunhandledrejectionHandler(reason, promise) {
		if (promise != null && promise.then != null) {
			/* First argument is an error. */
			handleUnhandledRejection(null, {error: reason, promise: promise});
		} else {
			/* First argument is an event. */
			handleUnhandledRejection(reason);
		}

	}

	function onrejectionhandledHandler(promise) {
		if (promise.then != null) {
			/* First argument is a Promise. */
			let errorData = store.find(promise);

			if (errorData != null) {
				handleRejectionHandled(null, errorData);
			}
		} else {
			/* First argument is an event. */
			handleRejectionHandled(promise);
		}

	}

	function configureContextHandlers(context) {
		if (typeof context.onunhandledrejection === "function") {
			debug("Wrapping previous handler for <context>.onunhandledrejection");
			let _oldHandler = context.onunhandledrejection;
			context.onunhandledrejection = function(reason, promise) {
				onunhandledrejectionHandler(reason, promise);
				_oldHandler(event);
			}
		} else {
			context.onunhandledrejection = onunhandledrejectionHandler;
		}

		if (typeof context.onrejectionhandled === "function") {
			debug("Wrapping previous handler for <context>.onrejectionhandled");
			let _oldHandler = context.onrejectionhandled;
			context.onrejectionhandled = function(promise) {
				onrejectionhandledHandler(promise);
				_oldHandler(promise);
			}
		} else {
			context.onrejectionhandled = onrejectionhandledHandler;
		}
	}

	/* Bundlers like Webpack will shim `process`, but set its `.browser` property to `true`. */
	let isWebWorker = (typeof WorkerGlobalScope !== "undefined");
	let isNode = (typeof process !== "undefined" && process.browser !== true);
	let isBrowser = (!isNode && !isWebWorker && typeof document !== "undefined");

	if (isNode) {
		debug("Detected environment: Node.js");

		/* Bluebird, ES6 in Node.js */
		process.on("unhandledRejection", (error, promise) => {
			let errorData = {
				error: error,
				promise: promise
			};

			handleUnhandledRejection(null, errorData);
		});

		process.on("rejectionHandled", (promise) => {
			let errorData = store.find(promise);

			if (errorData != null) {
				handleRejectionHandled(null, errorData);
			}
		});
	} else if (isWebWorker) {
		debug("Detected environment: WebWorker");

		/* Yaku, Bluebird, WHATWG Legacy(?)
		 * The Bluebird documentation says self.addEventListener, but it seems to use on* handlers instead. */
		configureContextHandlers(self);

		/* WHATWG */
		self.addEventListener("unhandledrejection", handleUnhandledRejection);
		self.addEventListener("rejectionhandled", handleRejectionHandled);

		/* WhenJS (note the capitalization) - currently broken */
		self.addEventListener("unhandledRejection", handleUnhandledRejection);
		self.addEventListener("rejectionHandled", handleRejectionHandled);
	} else if (isBrowser) {
		debug("Detected environment: Browser");

		if (window.addEventListener != null) {
			debug("addEventListener is available, registering events...");

			/* Bluebird, WHATWG */
			window.addEventListener("unhandledrejection", handleUnhandledRejection);
			window.addEventListener("rejectionhandled", handleRejectionHandled);

			/* WhenJS (note the capitalization) - currently broken */
			window.addEventListener("unhandledRejection", handleUnhandledRejection);
			window.addEventListener("rejectionHandled", handleRejectionHandled);
		}

		/* We will need to attempt to catch unhandled rejections using both the modern and
		 * legacy APIs, because Yaku only supports the latter, *even* in modern browsers.
		 */
		debug("Configuring window.on* handlers...");

		/* Bluebird (Legacy API), WHATWG (Legacy API), Yaku */
		configureContextHandlers(window);
	}

	return emitter;
}