Moving beyond console.log() — 8 Console Methods You Should Use When Debugging JavaScript and Node

Improve your JavaScript and Node debugging with these 8 powerful console methods beyond console.log(). Learn how to use console.assert(), console.table(), and more to find bugs faster.

Picture by Marco

The Console API

Every JavaScript developer has used console.log(‘text’). The console module is one of the most common utilities in JavaScript, and the API implemented in Node:

This is the definition written in the Node.js documentation page for the Console module 😅. However, beginners are prone to consult online tutorials instead of reading the documentation while starting with new technologies, missing the chance to learn how to properly use this new tool to 100% of its potential.

When talking about the Console API, newbies usually use only some functions like 👌console.log(), ⚠️ console.warn(), or ❌ console.error() to debug their application, while often there are many other methods which can perfectly implement our requirements and improve debugging efficiency.

This article is made to expose some of the most interesting console methods with related examples that I use while teaching at Codeworks. So let’s see a list of the 8 best functions from the Console module!

All the following methods are available in the global instance **console**, so it is not necessary to require the console module.

console.assert

The console.assert function is used to test if the passed argument is a truthy or falsy value. In the case that the passed value is false, the function logs the extra arguments passed after the first one, otherwise, the code execution proceeds without any log.

/*
 * Truthy values, nothing will be logged!
 */
console.assert(1, 'Doh, is a falsy value');
console.assert(true, 'Doh, is a falsy value');
console.assert('hello world', 'Doh, is a falsy value');

/*
 * Falsy values, assertion failed logged!
 */
console.assert(0, 'Doh, 0 is a falsy value');
// Assertion failed: Doh, 0 is a falsy value
console.assert(false, 'Doh, false a falsy value');
// Assertion failed: Doh, false a falsy value
console.assert('', 'Doh, an empty string is a falsy value');
// Assertion failed: Doh, an empty string is a falsy value

The assert method is particularly useful whenever you want to check the existence of values while keeping the console clean (avoid logging a long list of properties, etc.).

console.count

These two methods are used to set and clear a counter of how many times a particular string gets logged in the console:

/*
 * Print on the console the number of times the label "Hello" has been logged.
 */
console.count('Hello'); // Hello: 1
console.count('Hello'); // Hello: 2
console.count('Hello'); // Hello: 3

/*
 * Reset to zero the counter for a label.
 */
console.countReset('Hello');
/*
 * If now you call again the count for the "Hello" label, it will restart from 1.
 */
console.countReset('Hello'); // Hello: 1

console.group and console.groupEnd

.group and .groupEnd create and end a group of logs in your console. You can pass a label as the first argument of .group() to describe what it is concerned about:

console.table 📋

This particular method is incredibly useful to describe an object or array's content in a human-friendly table:

// Array of users
const users = [
  { name: 'Marco', age: 26 },
  { name: 'Leo', age: 24 },
];

// Log table with the user's information
console.table(users);

// Result on the console:
┌─────────┬─────────┬─────┐
│ (index) │  name   │ age │
├─────────┼─────────┼─────┤
│    0    │ 'Marco' │ 26  │
│    1    │  'Leo'  │ 24  │
└─────────┴─────────┴─────┘

console.table makes it easier for the inspection and logging of nested and complex arrays/objects.

console.time and console.timeEnd

In the case that you want to check the performance of your code in execution time, and to solve it you create a start timestamp with the Date API and use it to compute the difference after your code execution. Something like this:

const start = Date.now();

// do something...

const diff = Date.now() - start;
console.log('Time execution: ' + diff + ' ms');

// Time execution: <number> ms

Well, using the time and timeEnd functions, it is not necessary to do this trick. You can create your timing report simply by doing:

// BEFORE
const start = Date.now();
for (let i = 0; i < 10000000; i++) {
  1 + 1; // do something...
}
const diff = Date.now() - start;
console.log('Time execution with Date.now: ' + diff + ' ms');
// Time execution with Date. now: 12 ms

// AFTER
console.time('Time execution with console.time');
for (let i = 0; i < 10000000; i++) {
  1 + 1; // do something...
}
console.timeEnd('Time execution with console.time');
// Time execution with console. time: 11.4140625ms

Summary

With only 3 minutes of your time, you now have a larger scope of some of the wonderful tools available in the Console API. Integrate them with your debugging habits and your development speed will increase exponentially!

Last updated: Tue Sep 17 2019