/* Code-Comments */

Conditionally Render Components in React

October 26, 2019

I still remember when I first learned how to conditionally render my React components. It was a light bulb moment. I began seeing new opportunities to use this super power all over the place.

Using it is relatively simple. Let’s take a look at two different approaches within a class component:

  1. A ternary within the render’s return
  2. Variable assignment for a simpler return.

Ternary Approach

When we’re within the return statement of a React component (this is true for both a React class component’s render lifecycle method or the return statement within a functional component), we are able to evaluate Javascript expressions by using {}.

This means that we have access to the full power of the language with the notable exception of variable assignment.

It also proves to be fertile ground for ternaries.1

For example, let’s look at a React component that will show a form when the user clicks on a button (and presumably hides it if a different button is clicked within the form):

import React from 'react'
import ReactDOM from 'react-dom'

import './styles.css'

class App extends React.Component {
  constructor(props) {
    super(props)
    this.state = {
      showForm: false,
    }
  }

  toggleShow = () => {
    this.setState({ showForm: !this.state.showForm })
  }

  render() {
    return (
      <div className="App">
        {this.state.showForm ? (
          <div>
            form, click to hide
            <button onClick={this.toggleShow}>Hide</button>
          </div>
        ) : (
          <div>
            click to see form
            <button onClick={this.toggleShow}>Show</button>
          </div>
        )}
      </div>
    )
  }
}

const rootElement = document.getElementById('root')
ReactDOM.render(<App />, rootElement)

Zooming in on the return statement, it summarizes to this:

return this.state.showForm
  ? true /* Show the form */
  : false /* Hide the form, show the button */

Here we see that if showForm is true, we’ll show the form, if it’s not, it’ll be the button.

Variable Assignment

If the component grows in size / complexity, it’s quite possible that it may make more sense to extract the logic into the body of the Component (i.e. outside of the return):

class App extends React.Component {
  constructor(props) {
    super(props)
    this.state = {
      showForm: false,
    }
  }

  toggleShow = () => {
    this.setState({ showForm: !this.state.showForm })
  }

  render() {
    let RenderedComponent
    if (this.state.showForm) {
      RenderedComponent = (
        <div>
          form, click to hide
          <button onClick={this.toggleShow}>Hide</button>
        </div>
      )
    } else {
      RenderedComponent = (
        <div>
          click to see form
          <button onClick={this.toggleShow}>Show</button>
        </div>
      )
    }

    return <div className="App">{RenderedComponent}</div>
  }
}

const rootElement = document.getElementById('root')
ReactDOM.render(<App />, rootElement)

The return statement is now much simpler and it’s possible to extract the defintiions of our different components into other files to clean this up further and make it easier to read.2

Footnotes

  • 1 Ternaries are the terse if/then/else that take the format of <boolean evaluation> ? <if true> : <if false>.
  • 2 I put together a CodeSandbox to demonstrate this final state of conditional rendering. Check it out! I also refactored it after writing about setting state in different component types. I now have all three component types side-by-side for comparison.

Stephen Weiss

Thanks for reading! My name's Stephen Weiss. I live in Chicago with my wife, Kate, and dog, Finn.
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