What is conditional rendering

There are times when something should render in some situations and not in others. In frameworks like Vue, Angular and Svelte you have things like directives that directly add semantic ways to express this, React leans hard on using pure javascript to control the flow of a component (so strong Javascript skills really pay off in React).

In this article, we will look at an IsEven component that renders one thing if a prop is even and another it isn't. We'll show you different ways of express it.

Return statement within an if block

const IsEven = props => {
  if (props.number % 2 === 0) {
    return <h1> It is even </h1>
  } else {
    return <h1>It is odd</h1>
  }
}

Single Return Statement, If assigns value to a variable

const IsEven = props => {
  let result

  if (props.number % 2 === 0) {
    result = <h1> It is even </h1>
  } else {
    result = <h1>It is odd</h1>
  }

  return result
}

Returning a Ternary Operator

const IsEven = props => {
  return props.number % 2 === 0 ? <h1> it is even </h1> : <h1> it is odd </h1>
}

Returning a Ternary Operator but parts stored in variables

const IsEven = props => {
  const condition = props.number % 2 === 0

  const ifTrue = () => <h1> it is even </h1>

  const ifFalse = () => <h1> it is odd </h1>

  return condition ? ifTrue() : ifFalse()
}

Conditional Classes

const Modal = props => (
  <div className={props.visible ? "active" : ""}>{props.children}</div>
)

const Modal = props => {
  const divClass = props.visible ? "active" : ""

  return <div className={divClass}>{props.children}</div>
}

Conditional Styles

const Modal = props => (
  <div style={{ display: props.visible ? "block" : "none" }}>
    {props.children}
  </div>
)

const Modal = props => {
  const divDisplay = props.visible ? "block" : "none"

  return <div style={{ display: divDisplay }}>{props.children}</div>
}

const Modal = props => {
  const divStyle = {
    display: props.visible ? "block" : "none",
  }

  return <div style={divStyle}>{props.children}</div>
}

Using Object Keys to Determine JSX

const Component = props => {
  const result = {
    good: <h1>Good</h1>,
    bad: <h1>Bad</h1>,
    ugly: <h1>Ugly</h1>,
  }

  return result[props.key]
}

Using a Switch Statement

const Hello = (props) => {
  switch(props.language){
    case "eng":
      return <h1>Hello</h1>
    case "esp":
      return <h1>Hola</h1>
    default:
      return: <h1> No Language Detected </h1>
  }
}

React Conditional Rendering