JavaScript Fast Tips (II) - Styles in console output

Written on April 6, 2019

Category: JavaScript

Picture from Unsplash, by @danielwatsondesign
Picture from Unsplash, user Daniel Watson @danielwatsondesign

The previous Tuesday I was practicing with JavaScript and using console.log() to show data (nothing serious, if it was important I had used breakpoints, of course :-P), and in an outflow of extensive information, I remembered a nice way to organize it visually: You could give color and shape to the information displayed through console.log().


Then I remembered the first time I saw the Facebook console.log announcement (years ago) AFAIK my first experience of seeing a stylized console output. The key? the use of the -%c- directive as a parameter. Yes, you can use the %c directive to apply a CSS style to console output.

Javascript Warning through Console by Facebook
STOP! - Javascript Warning through Console by Facebook

When we’re using the directive -%c- we are indicating that the parameter that we’ll add next will be CSS guidelines that will have to be interpreted starting from the appearance of the directive.

Example 1

console.log("%cBEWARE OF THE DOG", "color: red; font-size: 3rem; font-weight:bold;");

Console Style example one

Example 2

Ok, but we can combine the style guidelines so that they apply only to certain parts of the text (not just the entire string). Let’s see.

console.log("This is a partial %cStylized message", "color: green; font-style: italic; font-size: 4rem; background-color: yellow; padding: 2px");

Console Style example two

Example 3

We can extend the CSS rules application as much as we want to style our console information.

        "%cPROTECT YA NECK!",
        "color:blue;font-family:system-ui;font-size:4rem;-webkit-text-stroke: 4px black;font-weight:bold"

Console Style example three

Example 4

We can also integrate CSS values within properties into objects that we can use by calling them from console.log().

  let colors = {
    "gray": "font-weight: bold; color: #1B2B34;",
    "red": "font-weight: bold; color: #EC5f67;",
    "orange": "font-weight: bold; color: #F99157;",
    "yellow": "font-weight: bold; color: #FAC863;",
    "green": "font-weight: bold; color: #99C794;",
    "teal": "font-weight: bold; color: #5FB3B3;",
    "blue": "font-weight: bold; color: #6699CC;",
    "purple": "font-weight: bold; color: #C594C5;",
    "brown": "font-weight: bold; color: #AB7967;"
  let backgrounds = {
     "black": "background: black; color: white; display: block;",
     "blue": "background: blue; color: white; display: block;",
     "red": "background: red; color: white; display: block;",
     "yellow": "background: yellow; color: white; display: block;",
     "green": "background: green; color: white; display: block;",
     "pink": "background: pink; color: white; display: block;"
// All the colors
  console.log('%cHello One', colors.gray);
  console.log('%cHello Two',;
  console.log('%cHello Three',;
  console.log('%cHello Four', colors.yellow);
  console.log('%cHello Five', colors.teal);
  console.log('%cHello Six',;
  console.log('%cHello Seven', colors.purple);
  console.log('%cHello Eight', colors.brown);

// All the backgrounds
  console.log('%cThis is the black background',;
  console.log('%cThis is the blue background',;
  console.log('%cThis is the red background',;
  console.log('%cThis is the yellow background', backgrounds.yellow);
  console.log('%cThis is the green background',;
  console.log('%cThis is the pink background',;

Console Style example four

Example 5

Let’s play a little with the styles.

  var styles = [
      'background: linear-gradient(#D33106, #571402)'
      , 'border: 1px solid #3E0E02'
      , 'color: white'
      , 'display: block'
      , 'text-shadow: 0 1px 0 rgba(0, 0, 0, 0.3)'
      , 'box-shadow: 0 1px 0 rgba(255, 255, 255, 0.4) inset, 0 5px 3px -5px rgba(0, 0, 0, 0.5), 0 -13px 5px -10px rgba(255, 255, 255, 0.4) inset'
      , 'line-height: 40px'
      , 'text-align: center'
      , 'font-weight: bold'

  console.log('%c This is just a special log message', styles);

Console Style example five

Example 6

Now, we’re going to create an external function to print Style in console, encapsulating the calling to console.log().

function myCustomLog(message, color="black") {
  switch (color) {
    case "info":
      color = "Green";
      fontsize = "2rem";
    case "success":
      color = "Blue";
      fontsize = "3rem";
    case "warning":
      color = "Orange";
      fontsize = "4rem";
    case "error":
      color = "Red";
      fontsize = "5rem";
      color = color;
      fontsize = "1rem";

  console.log(`%c${message}`, `color:${color}; font-size:${fontsize};`);

myCustomLog("Calling to my custom log without a color value, using default");
myCustomLog("Take more Info...", "info");
myCustomLog("Now, a Success! message", "success");
myCustomLog("This is a Warning!!", "warning");
myCustomLog("Gets an Error!", "error");

Console Style example six

Well, here we come with this quick post about applying CSS styles to console.log(). If you are interested, I have created a folder in a Gitlab repository and a specific branch for these and other console tips. Here In the file called “tips_tricks_console.js” you will find the examples.


Greetings. wq! :-*

Written on April 6, 2019