Why do script errors

Thank you for supporting the partners who make SitePoint possible. It declares a single function, foo, whose invocation will always throw a ReferenceError. When this document is loaded in the browser, and JavaScript is executed, the following is output to the console logged via the window.

For this reason, browsers only give window. All we know is that an error occurred — nothing else! You may receive an unresponsive script error, as the page continues slowly attempting to load. A script error may be the result of problems within the source code on the page, or it could be a problem with your system or your system settings. If your computer, or certain elements of it are outdated, or if your settings are faulty, you will likely see a number of errors. Settings on your computer or within your network may have been adjusted to block things like Java Applets or Active X controls.

Changing the settings, if allowable, may relieve the problem. A script error is often a nuisance rather than a serious problem. Certain operating systems or browsers may have glitches of their own or may be in need of updates.

This means that in most cases, JavaScript files will be served from a different origin than the website itself as the CDN will use a different domain. If your website has a lot of application code defined in JavaScript files hosted on CDNs and a runtime error happens, the error description that hits the window. So how do we fix this, or more precisely, how do we get detailed information for errors that originate in scripts served from a different origin? This is a two step process, we need to make changes both on our website and on the third-party origin.

If you are trying to load a script on your website from a different origin and add the script tag like the one below, the browser will refuse to load the script. Most CDNs will do this by default as their main purpose is serving static files to other origins, but if you are running your own servers for serving static files, they will need to return the following HTTP header for static files:.

This will enable browsers to fetch static files from this server from any domain. If you have a known list of domain you want to allow, for example if your website is at www.

If you are a developer and you have run into this issue, and you need a quick fix, you could use a web proxy such as CORS Anywhere. The proxy server forwards the requests to the third-party server, and then sends them back to your website with the CORS headers added.

There are some browser quirks that you should be aware of. What we wrote above applies to the latest browser, or more specifically to:.

Firefox has different behavior for runtime errors. These will be provided to the onerror callback without any obfuscation, even if the script is served from a different origin. Syntax errors will be blocked though if the CORS headers are missing.