Resolving the ‘Unexpected Console Statement’ Warning: A Step-by-Step Guide

by
Unexpected Console Statement
LinkedIn

In JavaScript development, encountering an ‘unexpected console statement‘ warning is a common experience, especially when using a linter tool like ESLint. The warning says that a piece of code, typically a console.log(), console.warn(), or console.error() has been detected and to alert the potential debugging information that could be exposed. However, there are some scenarios in which we might intentionally use console statements to get more details.

In this article, We will understand the error and learn techniques including configuring the linter rules to allow console statements in certain parts of the code or disabling the rule entirely if it doesn’t align with the project’s requirements.

Understanding Console Statements in JavaScript

Purpose and Usage of Console Statements

Console Statements serve the primary function of displaying information as a console output, which helps to understand the flow of the execution and inspect the values of variables at a given moment. The most common method, console.log(), prints the standard messages to the console, while methods like console.info(), console.error(), and console.warn() categorize the output as informational, error, or warning messages, respectively.

Common Types of Console Statements

  • log: The most basic form, it outputs general messages.
  • info: Denotes an informational message, often displayed with an i icon.
  • error: Outputs error messages, highlighted with a red color or error icon.
  • warn: Shows a warning message, typically with a yellow warning sign.
  • trace: Provides a stack trace to the point of the method call, which is useful for identifying the path execution has taken.

Replicating ‘Unexpected Console Statement’ Warning

To replicate the “unexpected console statement” Warning, you typically need to have a linter set up in your environment that is configured to flag console statements as issues. Linters like ESLint are widely used in JavaScript projects for this purpose.

Here’s a step-by-step guide on how to replicate this warning:

Step 1: Set Up Your Project

If you don’t already have a project set up, create a new directory for your project and initialize it with npm (Node Package Manager), which will create a package.json file for you.

mkdir my_project 

cd my_project 

npm init -y

Example:

# npm init -y
Wrote to /root/my_project/package.json:

{
  "name": "my_project",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC"
}

Note: If you do not have the npm package, Install using yum or equivalent package manager

# yum install npm

Step 2: Install ESLint

Install ESLint in your project as a development dependency.

# npm install eslint --save-dev


added 99 packages, and audited 100 packages in 3s

23 packages are looking for funding
  run `npm fund` for details

found 0 vulnerabilities
npm notice 
npm notice New major version of npm available! 8.19.4 -> 10.5.0
npm notice Changelog: https://github.com/npm/cli/releases/tag/v10.5.0
npm notice Run npm install -g npm@10.5.0 to update!
npm notice

Step 3: Initialize ESLint

Run the ESLint initialization command and follow the prompts to set up your linting configuration. If you’re unsure about the options, you can select the defaults or choose as below

# npx eslint --init

You can also run this command directly using 'npm init @eslint/config'.
Need to install the following packages:
  @eslint/create-config@0.4.6
Ok to proceed? (y) 
✔ How would you like to use ESLint? · problems
✔ What type of modules does your project use? · esm
✔ Which framework does your project use? · none
✔ Does your project use TypeScript? · No / Yes
✔ Where does your code run? · browser
✔ What format do you want your config file to be in? · JavaScript

Step 4: Configure ESLint to Flag Console Statements

After initialization, ESLint will create a .eslintrc file in your project root. Open this file and ensure it includes a rule to flag console statements. If it doesn’t, you can add it manually:

{
  "rules": {
    "no-console": "warn" // Or "error" to treat console statements as an error
  }
}

Example:

]# cat .eslintrc.js 
module.exports = {
    "env": {
        "browser": true,
        "es2021": true
    },
    "extends": "eslint:recommended",
    "overrides": [
        {
            "env": {
                "node": true
            },
            "files": [
                ".eslintrc.{js,cjs}"
            ],
            "parserOptions": {
                "sourceType": "script"
            }
        }
    ],
    "parserOptions": {
        "ecmaVersion": "latest",
        "sourceType": "module"
    },
    "rules": {
    "no-console": "warn"
  }

}

Step 5: Write Some Code

Create a JavaScript file in your project and add a console statement to it. For example, create index.js and add the following:

console.log('This is a console statement.');

Step 6: Run ESLint

Run ESLint on your project:

npx eslint .

Step 7: Observe the Warning

If the above setup is done properly you will see the ERROR about the unexpected console statement in index.js. 

# npx eslint .


/root/my_project/index.js
  1:1  warning  Unexpected console statement  no-console

✖ 1 problem (0 errors, 1 warning)

This warning is ESLint’s way of telling you that it found a console statement in your code, which is against the rules specified in your .eslintrc configuration file. The purpose of such a rule is typically to prevent us from leaving debugging statements in production code, as mentioned earlier.

Handling ‘Unexpected Console Statements‘

To handle the “unexpected console statement” warning highlighted by ESLint in your JavaScript code, you have a few different approaches depending on your intention and the context in which the console statement is used. Here are some methods to consider:

1. Remove the Console Statement

If the console statement was used for debugging purposes and is no longer needed, simply remove or comment it out:

Before:

console.log('This is a console statement.');

After:

// console.log('This is a console statement.');

2. Use a Different Logging Mechanism

For situations where logging is necessary (e.g., error logging in production), consider using different logging mechanisms that can be enabled or disabled based on the environment. This way, you can avoid console logs in production while still capturing important information:

if (process.env.NODE_ENV === 'development') {
    console.log('Log this message only in development');
}

3. Adjust ESLint Rules

If you have a valid reason to keep console statements in your code (such as logging in a development environment or specific logs that are required in production), you can adjust your ESLint rules to allow console statements under certain conditions or ignore them entirely.

To allow console statements globally, modify your .eslintrc file:

{
  "rules": {
    "no-console": "off"
  }
}

Or, to disable the rule only for specific files or lines, use ESLint comments:

Disable for a specific line:

// eslint-disable-next-line no-console
console.log('This is a console statement.');

Disable for an entire file:

/* eslint-disable no-console */
console.log('This is a console statement.');

Conclusion

The “unexpected console statement” warning helps as a reminder to make sure your code is clean and production-ready. Whether you choose to remove the console statements, adjust your ESLint configuration, or implement an alternative logging mechanism, the key is to ensure that your final code aligns with your project’s standards and requirements.

Happy Learning !!

Jerry Richard
Follow me
Latest posts by Jerry Richard (see all)

Was this post helpful?

Yes
No
Thanks for your feedback!
LinkedIn

Leave a Comment