The Complete Guide to JavaScript console.log() with Examples

Printing messages in the browser console have definitely come to rescue to all the developers out there. c**onsole.log( )** messages are like medicines for most of your diseases while debugging some wired problems in your code.

Most of the devs out there are like — Let’s print the message in the browser to know more about this issue. I’m sure that I’m not the only one doing this. 🤪

Apart from the most commonly used console.log( ) message to print the message in the browser there are plenty of different ways to make your debugging process a lot easier. Let’s take a look at them one by one with examples.

console.log( ) | info( ) | debug( ) | warn( ) | error( )

These will directly print the raw string with appropriate color based on the type of event that is provided to them.

console log/info/debug/warn/error

Use placeholders

There are different placeholders that can be used as listed below
%o — which takes an object,
%s — which takes a string, and
%d — which is for a decimal or integer

placeholders

Add CSS to console messages

Do all of your console messages look the same? well, it won’t be the same from now on, make your logs look more catchy for what matters the most to you.

Messages with colors

What to color only a specific word from the log message? Here you go 😄

highlighting specific word

console.dir( )

Prints a JSON representation of the specified object.

HTML elements in console

Get the HTML elements in the console just like inspecting elements

HTML Elements

console.table ( )

Want to view JSON in a proper and easily understandable way?

Better visualization of an array of objects huh!

console.group( ) & console.groupEnd( )

It is quite possible to group the messages with the console

Grouping messages

console.count( )

This function logs the number of times that this particular call to count() has been called. This function takes an optional argument label.

If label is supplied, this function logs the number of times count() has been called with that particular label.

If label is omitted, the function logs the number of times count() has been called at this particular line.

counter

console.assert( )

This comes quite handy when you only want to print some selected logs i.e. it will only print the false argument. It does nothing at all if the first argument is true.

Assertion

console.trace( )

This method displays a trace that shows how the code ended up at a certain point.

Trace

console.time( )

A dedicated function for tracking the time taken for actions, console.time() is a better way to track the microtime taken for JavaScript executions.

console.memory( )

Wondering how our JavaScript applications are using browser memory?

Memory

console.clear( )

This one is the last but not the least 😁, To clear all the above console messages which you’ve learned, It’s time to destroy them with clear() command

Here is the gist for all above snippets
Link — https://gist.github.com/Harshmakadia/fc25e56cb8f49145f4c9b3528f04215f

// time and time end
console.time("This");
let total = 0;
for (let j = 0; j < 10000; j++) {
  total += j
}
console.log("Result", total);
console.timeEnd("This");

// Memory
console.memory()

// Assertion
const errorMsg = 'Hey! The number is not even';
for (let number = 2; number <= 5; number += 1) {
    console.assert(number % 2 === 0, {number: number, errorMsg: errorMsg});
}

// Count
for (let i = 0; i < 11; i++) {
  console.count();
}

// group & groupEnd
console.group();
  console.log('Test message');
  console.group();
    console.log('Another message');
    console.log('Something else');
  console.groupEnd();
console.groupEnd();


// Table
const items = [
  {
    name: "chair",
    inventory: 5,
    unitPrice: 45.99
  },
  {
    name: "table",
    inventory: 10,
    unitPrice: 123.75
  },
  {
    name: "sofa",
    inventory: 2,
    unitPrice: 399.50
  }
];
console.table(items)

// Clear
console.clear()

// HTML Element
let element = document.getElementsByTagName("BODY")[0];
console.log(element)

// Dir
const userInfo = {"name":"John Miller", "id":2522, "theme":"dark"}
console.dir(userInfo);

// Color
console.log('%cColor of the text is green plus small font size', 'color: green; font-size: x-small');

// pass object, variable
const userDetails = {"name":"John Miller", "id":2522, "theme":"dark"}
console.log("Hey %s, here is your details %o in form of object", "John", userDetails);

// Default 
console.log('console.log');
console.info('console.info');
console.debug('console.debug');
console.warn('console.warn');
console.error('console.error');

Happy Learning! 💻 😀

#JavaScript #WebDev