Today i’have created a simple class to log in the backend the javascript error, so i can have a real time monitoring of how error appear to the users.

We can use a window.onerror and the addEventListener rewrite.

Window.onerror has been available in most browser, but the argument that are passed on each browser are different:

Browser	Message	URL	lineNo	colNo	errorObj
Firefox	✓	✓	✓	✓	✓
Chrome	✓	✓	✓	✓	✓
Edge	✓	✓	✓	✓	✓
IE 11	✓	✓	✓	✓	✓
IE 10	✓	✓	✓	✓
IE 9, 8	✓	✓	✓
Safari 10 and up	✓	✓	✓	✓	✓
Safari 9	✓	✓	✓	✓
Android Browser 4.4	✓	✓	✓	✓

This is my class with a _wrap function, and a SendError that trasmit the data on the backend

class ErrorHandler {

	constructor() {
		let $this = this;
		$this._prototypeInit();

		window.onerror = function (message, file, line, col, error) {
			let data = message+" from "+error.stack;
			$this.SendError(data);
		};
	}

	_prototypeInit() {
		let $this = this;
		var addEventListener = window.EventTarget.prototype.addEventListener;
		window.EventTarget.prototype.addEventListener = function (event, callback, bubble) {
			addEventListener.call(this, event, $this._wrap(callback), bubble);
		}
		var removeEventListener = window.EventTarget.prototype.removeEventListener;
		window.EventTarget.prototype.removeEventListener = function (event, callback, bubble) {
			removeEventListener.call(this, event, callback._wrapped || callback, bubble);
		}
	}

	_wrap(func) {
		let $this = this;
		if (!func._wrapped) {
			func._wrapped = function () {
				try {
					func.apply(this, arguments);
				} catch (e) {
					let data = e.message+" from "+e.stack;
					$this.SendError(data);
					throw e;
				}
			}
		}
		return func._wrapped;
	}

	SendError(message) {
		let $this = this;
		fetch('/ErrorHandler/WriteLog', {
			method: 'POST',
			body: JSON.stringify({ message: message }),
			headers: {
				'Content-Type': 'application/json'
			}
		}).then(res => res.json()).catch(error => console.error('Error:', error));
	}
}

In the message we put the stacktrace.
To use it at the init of your application:
let handlerError = new HandlerError();

Write to me if you have some suggestion to improve it.