window.onerror事件用来自定义错误处理

Event reference:      https://developer.mozilla.org/en-US/docs/Web/Events

http://w3c.github.io/html/webappapis.html#events

原文： https://developer.mozilla.org/en-US/docs/Web/API/GlobalEventHandlers/onerror

An event handler for the error event. Error events are fired at various targets for different kinds of errors:

• When a JavaScript runtime error (including syntax errors and exceptions thrown within handlers) occurs, an error event using interface ErrorEvent is fired at window and window.onerror() is invoked (as well as handlers attached by window.addEventListener (not only capturing)).
• When a resource (such as an <img> or <script>) fails to load, an error event using interface Event is fired at the element that initiated the load, and the onerror() handler on the element is invoked. These error events do not bubble up to window, but (at least in Firefox) can be handled with a single capturing window.addEventListener.

Installing a global error event handler is useful for automated collection of error reports.

Syntax

For historical reasons, different arguments are passed to window.onerror and element.onerror handlers (as well as on error-type window.addEventListenerhandlers).

window.onerror

window.onerror = function(message, source, lineno, colno, error) { ... }

Function parameters:

• message: error message (string). Available as event (sic!) in HTML onerror=""handler.
• source: URL of the script where the error was raised (string)
• lineno: Line number where error was raised (number)
• colno: Column number for the line where the error occurred (number)
• error: Error Object (object)

When the function returns true, this prevents the firing of the default event handler.

window.addEventListener('error')

window.addEventListener('error', function(event) { ... })

event of type ErrorEvent contains all the information about the event and the error.