When I was inspecting some code on Facebook. I came across this interesting feature. A simple styled console warning message from Facebook to its dear users(products).

Facebook's console warning message states like this;

Stop!

This is a browser feature intended for developers. If someone told you to copy and paste something here to enable a Facebook feature or "hack" someone's account, it is a scam and will give them access to your Facebook account.

See https://www.facebook.com/selfxss for more information.

So in this tutorial below, I will help you or show you how to recreate the same console warning as Facebook on your website.

Tutorial.

Now, what is %c?

The %c applies CSS style rules to the console log output string as specified by the second parameter as seen in the example below.

var stopCss = "color:red; font-size:65px; font-weight:bold; -webkit-text-stroke: 1px black";
var msgCss = "font-size:20px; background-color:teal;";

console.log('%cStop', stopCss);
console.log('%cThis feature is intended for Developers only.', msgCss);
console.log('%cSee https://ostoncodecypher.com/about for more info.', msgCss);
	

If I am to explain the example above;

%c is the specifier that’s within the first argument of the console.log() which picks up the very next argument as CSS style for the %c pattern argument text.

'Stop' + other texts in other console.log()s are the messages

Then finally stopCss and msgCss are the variables holding the CSS styles.