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

Incredible Demos

  • By
    HTML5 Input Types Alternative

    As you may know, HTML5 has introduced several new input types: number, date, color, range, etc. The question is: should you start using these controls or not? As much as I want to say "Yes", I think they are not yet ready for any real life...

  • By
    MooTools Window Object Dumping

    Ever want to see all of the information stored within the window property of your browser? Here's your chance. The XHTML We need a wrapper DIV that we'll consider a console. The CSS I like making this look like a command-line console. The MooTools JavaScript Depending on what you have loaded...

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!