May 22, 2021

Conditional class names in Reactjs without pain

Sambit Sahoo

I’ve been working on multiple Reactjs projects for the last few months. Coming from a strong Vuejs background, it wasn’t that hard for me to catch the basic concepts of the very popular library. Under the hood they work on the same battle-tested concept i.e. Virtual DOM. Even though Vue has support for JSX, the experience is far better with React . It really feels amazing to write everything with the same language, but there are some trade-offs that are hard to ignore.

Out of the many reasons why most of the Vue developers find it uncomfortable to switch to React, conditional rendering is a fairly important one. It’s really very intuitive in Vuejs to render something based on some conditions without leaving your html.

<h1 v-if="isDay" >I'm rendered during day</h1>
<h1 v-else>Else I'm rendered</h1>

It’s also the same experience while doing conditional rendering in React without leaving JSX by using the ternary operator.

{ isDay ?
  (<h1>I'm rendered during day</h1>):
  (<h1>Else I'm rendered</h1>)

But where the Vue really shines in terms of conditional rendering is when doing it with css classes. e.g.

<h1 :class="{'text-red': isRed}" >I'm red.</h1>
<h1 :class="{'text-red': !isRed}" >I'm not red.</h1>

The React way with js template literals e.g.

<h1 className={`${isRed ? 'text-red': ''}`} >I'm red.</h1>
<h1 className={`${!isRed ? 'text-red': ''}`} >I'm not red.</h1>

As we can see in above examples, in Vue it’s a bit more intuitive to use css classes conditionally. In React it won’t be that much troublesome when there are a few number of css classes on a HTML element. But when there are multiple css classes and you want to use selective css classes conditionally, it’ll lead to a not-so-good looking code with template literals. e.g.

<div className={`modal ${!isModal ? 'opacity-0 pointer-events-none' : ''}  fixed w-full h-full top-0 left-0 flex items-center justify-center`}

There is a npm package which solves this issue by providing a helper method to write conditional css classes. You can do the same without installing the package with just 4-5 lines of code.

export function classNames(classes: Record<string, boolean>) {
  const toBeClasses = Object.keys(classes).map((key) =>
    classes[key] === true ? key : '',
  return toBeClasses.join(' ');

We can use the helper method to write conditional css classes in a more simpler way i.e.

// import {classNames} from './helpers'
        'flex items-center justify-center py-2 px-4 rounded-md max-w-xs lg:max-w-2xl drop-shadow-lg transition-all mb-2': true,
        'bg-green-400 text-white': type === 'success',
        'bg-red-400 text-white': type === 'error',
    <div className="text-md font-semibold">{message}</div>

This way it’s easier to have control over conditional css classes. The Typescript types can be removed to use this as a Javascript method.

Have a good day with React ⚛️. Peace ☮️