simple-merge-class-names

A straightforward utility for merging CSS class names in React (JSX) and other JavaScript projects.

For Production look into https://www.npmjs.com/package/clsx

Table of Contents

• simple-merge-class-names
  • Table of Contents
  • The Genocidal Occupation Is Starving Gaza
  • Installation
    • Recommended If Using VSCode: Install Prettier Extension
  • Usage
    • TypeScript Definitions
    • Valid Arguments
    • Invalid Arguments
    • Reason for warnings
    • Conditional class inclusion
    • Return Result
    • Chaining
  • Usage of Browser Debugger
  • VSCode Workflow To Minimize Typing Strain
  • Testing Source Code
    • Run Once
    • Run Watch Mode
  • License

The Genocidal Occupation Is Starving Gaza

• Donate

• (US) Demand Immediate Opening of ALL Gaza Border Crossings

• Boycott Brands Supporting Gaza Holocaust

• Legal Action

Palestine is about fundamental non-negotiable human rights. End all financial and diplomatic ties with i*rael.

Installation

pnpm add simple-merge-class-names

yarn add simple-merge-class-names

npm install simple-merge-class-names

Recommended If Using VSCode: Install Prettier Extension

• https://marketplace.visualstudio.com/items?itemName=esbenp.prettier-vscode

It will nicely format your code especially when you have lots of classes, and will significantly improve your visual experience.

If you have a different IDE use an equivalent auto code formatter tool/extension

Usage

Function	Prints console warnings	Activates debugger
mergeClassNames	✅	❌
mergeClassNamesDebugger	✅	✅

Example:

import { mergeClassNames } from "simple-merge-class-names";

const Component = ({ condition }) => {
    return (
        <div
            className={mergeClassNames(
                "app",
                condition ? "min-h-dvh" : false,
                "grid",
                "grid-rows-[auto_1fr_auto]",
                "outline"
            )}
        >
            Hello, world!
        </div>
    );
};

TypeScript Definitions

export declare const mergeClassNames: (
    ...args: (string | false)[]
) => string | false;

export declare const mergeClassNamesDebugger: (
    ...args: (string | false)[]
) => string | false;

Valid Arguments

Only 2:

1. Valid strings, not whitespace, of length >= 1

   (As long as you have content in the string you're OK)

2. false

Example, This is OK:

mergeClassNames(
    "mx-auto",
    "min-dvh    ",
    "   flex",
    "      grid      ",
    "italic     font-bold   ",
    `
        gap-y-4
    `,
    false,
    condition ? "daisy-btn-active" : false
);

Invalid Arguments

Each below argument will be ignored, and cause a Dev Console warning to be printed to alert you:

• Empty strings: (e.g. "")
• Whitespace any consecutive combination of the following:
  • new lines,
  • spaces,
  • tabs
  • (e.g. " ", "\n ", " \t \n ", etc.)
• true
• undefined
• null
• Objects
• Numbers
• Big Int
• Symbols

// Example: These arguments will be **ignored**, and a console.warn will be printed

const someVariable = "";

mergeClassNames(
    someVariable, // empty string
    "   ", // whitespace
    "\n ", // whitespace
    "  \t  \n ", // whitespace
    `           // whitespace
        \n
    `,
    true, // true
    undefined, // undefined
    null, // null
    {
        // object
        name: "value",
        email: "email@example.com",
    },
    123, // number
    123.45 // number
);

Reason for warnings

• To avoid silent failures, because you will be pulling your hair asking why a Tailwind class isn't working only to figure out you passed an object, array or an empty string instead of a valid string. (It could also be because of an unsupported class name or typo but this is beyond the scope of this package)

Conditional class inclusion

Use this pattern:

• condition ? "class-name" : false with false serving as the valid fallback.
• or condition === true ? "class-name" : false if you want to be specific.

Note: Avoid using the short-circuit implicit syntax like this:

• condition && "class-name", beside less readable code, it can produce falsy values which will be ignored (e.g. 0, "", undefined, and null).

import { mergeClassNames } from "simple-merge-class-names";

const Component = () => {
    return (
        <div
            className={mergeClassNames(
                "app",
                condition ? "min-h-dvh" : false,
                "grid",
                "grid-rows-[auto_1fr_auto]",
                "outline"
            )}
        >
            Hello, world!
        </div>
    );
};

Return Result

Either:

1. Valid string, never whitespace, always length >= 1

2. or false (if all input arguments were invalid)

Chaining

Because of safe return types you can chain calls safely without worrying about warnings or arguments being ignored.

So this is OK:

mergeClassNames(condition ? "disabled" : mergeClassNames(...) )

Usage of Browser Debugger

Once you see warnings in the console, the next step is to use mergeClassNamesDebugger

1. Enable Debugger
   • For chromium-based browsers it's On by default and you don't need to do anything AFAIK.
   • For Firefox: Open Developer Tools:
     • Make Sure Debugger (tab) -> Pause on debugger statement is ticked.
     • Keep Dev Tools open.

• Use import {mergeClassNamesDebugger as mergeClassNames} to debug the entire file, and keep the rest intact.

  import { mergeClassNamesDebugger as mergeClassNames } from "simple-merge-class-names";
  
  const Component = ({ condition }) => {
      return (
          <div
              className={mergeClassNames(
                  "app",
                  condition ? "min-h-dvh" : false,
                  "grid",
                  "grid-rows-[auto_1fr_auto]",
                  "outline"
              )}
          >
              Hello, world!
          </div>
      );
  };

• or call mergeClassNamesDebugger directly.

  import { mergeClassNamesDebugger } from "simple-merge-class-names";
  
  const Component = ({ condition }) => {
      return (
          <div
              className={mergeClassNamesDebugger(
                  "app",
                  condition ? "min-h-dvh" : false,
                  "grid",
                  "grid-rows-[auto_1fr_auto]",
                  "outline"
              )}
          >
              Hello, world!
          </div>
      );
  };

• Refresh the page, the debugger should connect:

  • Navigate to the Call stack
  • Click the function/component right before mergeClassNamesDebugger

  

• Hover over the arguments, one or several should be invalid:

VSCode Workflow To Minimize Typing Strain

Use single quotes around class names, and activate Prettier which will neatly format and arrange the classes.

• Install Prettier

• Enable Editor: Word Wrap:

  • Open Settings (UI) → Editor: Word Wrap → on
  • or User Settings (JSON) and add this entry "editor.wordWrap": "on"

• Use single quotes (') around class names

• Save the file

Before and after:

Testing Source Code

This project uses Vitest as the test runner for fast and modern testing.

Run Once

git clone https://github.com/new-AF/simple-merge-class-names
cd simple-merge-class-names
pnpm test

Run Watch Mode

pnpm test:watch

License

This project is licensed under the AGPL-3.0 License. See LICENSE.txt for full details.

---

Enjoy 😉