Add Styles to Console Statements

By  on  

I was recently checking out Google Plus because they implement some awesome effects.  I opened the console and same the following message:

WARNING!

Using this console may allow attackers to impersonate you and steal your information using an attack called Self-XSS.

Do not enter or paste code that you do not understand.

I wasn't surprised to see that message but what I did notice was that the text was red and the background was yellow.  The text was even a bit bigger.  How did they do it?  Pretty easily:

console.log("%c%s",
            "color: red; background: yellow; font-size: 24px;",
            "WARNING!");

The first argument is the order of style and message, the second is the style set, and the last is the desired message.

As to why you'd want to use this?  If it helps you identify debug information easier in the console, you may consider calling more attention to some messages!

Recent Features

  • By
    Responsive Images: The Ultimate Guide

    Chances are that any Web designers using our Ghostlab browser testing app, which allows seamless testing across all devices simultaneously, will have worked with responsive design in some shape or form. And as today's websites and devices become ever more varied, a plethora of responsive images...

  • By
    Designing for Simplicity

    Before we get started, it's worth me spending a brief moment introducing myself to you. My name is Mark (or @integralist if Twitter happens to be your communication tool of choice) and I currently work for BBC News in London England as a principal engineer/tech...

Incredible Demos

  • By
    MooTools Zebra Tables Plugin

    Tabular data can oftentimes be boring, but it doesn't need to look that way! With a small MooTools class, I can make tabular data extremely easy to read by implementing "zebra" tables -- tables with alternating row background colors. The CSS The above CSS is extremely basic.

  • By
    MooTools Accordion: Mouseover Style

    Everyone loves the MooTools Accordion plugin but I get a lot of requests from readers asking me how to make each accordion item open when the user hovers over the item instead of making the user click. You have two options: hack the original plugin...

Discussion

  1. Easy, if one controls the browser and therefor the console, that has to display this ;) But Firefox supports this as well, and only IE prints both, the format string as the string itself 1:1 into F12.

  2. There’s a JS library that makes styling comments much easier:

    https://github.com/astoilkov/console.message

  3. By replacing your formatting placeholders with %c%o, it will output a readable repr for any type of object you pass in, not just the str value.

    https://jsfiddle.net/jsatt/Lta6p2jz/2/

  4. very cool advice! my console is very colour ;)

  5. With some trickery you can inject images too!

    console.log("%cDuckie.TV", "color:transparent; font-size: 16pt; line-height: 125px; padding:25px; padding-top:30px; padding-bottom:60px; background-image:url(http://duckietv.github.io/DuckieTV/img/icon128.png); background-repeat:no-repeat; ", "quack!\n\n\n\n\n\n");
    
  6. Amelia BR

    I find it amusing that this post starts with an example of a warning not to copy & paste code into the console, and ends with me wanting to copy & paste code from people’s comments into the console.

    But it’s okay, cause I sort of understand it, right?

  7. schadeck

    I like to put an object at the top of my script when I am developing to create a shortcut for styling my logs:

    // for styling console.log
    // EXAMPLE: console.log(sty.sty, sty.red, 'thingToLog:' ,+ foo);
    var sty = {
        sty: '%c%s',
        grn: 'background:#9c9;color:#141;padding:.25em;line-height:1.5em;',
        ylw: 'background:#ff0;color:#993;padding:.25em;line-height:1.5em;',
        red: 'background:#c99;color:#411;padding:.25em;line-height:1.5em;',
        org: 'background:#da0;color:#830;padding:.25em;line-height:1.5em;',
        gry: 'background:#666;color:#fff;padding:.25em;line-height:1.5em;',
        prp: 'background:#97e;color:#405;padding:.25em;line-height:1.5em;',
        blu: 'background:#8ac;color:#036;padding:.25em;line-height:1.5em;'
    };
    

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!