Cleaner React: Conditional Rendering

Often times React components become hard to understand due to conditional rendering. At first a simple if/else or ternary operator appears benign to your overall readability, but over time as changes occur another if/else or ternary may be added.

Compounding this issue is when conditional operators are nested many times, which unfortunately is too easy to do.

Let's first look at how to conditionally render in React and then dive into several experiments that might present more readable ways to conditionally render in React.

Conditional Rendering Styles

Simple Scenario

Scenario:Show a login component vs a register component given the property "isLoggedIn"

Using &&

Used quite often the "&&"is easy to throw in for some quick conditional logic.

const Session = ({ isLoggedIn }) => {  return (   <>    {isLoggedIn && <Login />}    {!isLoggedIn && <SignOut />}   </>  );  };  

Using If/Else Statements

Given this simple scenario, a guard clause works here and is a bit more readable than the "&&".

const Session = ({ isLoggedIn }) => {  if (isLoggedIn) {   return <SignOut />  }  return <Login />  };  

Using Ternary Operator

This also is easier to understand; being able to one line this is pretty nice.

const Session = ({ isLoggedIn }) => isLoggedIn ? <SignOut /> : <Login />;  

Complex Scenario

Scenario: Show a login component vs a register component given the property "isLoggedIn", in addition show the "UnicornLogin" component if the "isUnicorn" flag is true.

Using &&

This is awful. It is clear that the "&&" is only good to use sparingly and only when there is one condition.

const Session = ({ isLoggedIn, isUnicorn }) => {  <>   {isLoggedIn && !isUnicorn && <Login />}   {!isLoggedIn && isUnicorn && <isUnicorn />}   {!isLoggedIn && !isUnicorn && <SignOut />}  </>;  };  

Using If/Else Statements

Less awful, but this is going to make things tricky if you ever wanted to wrap each of the components being returned with another component.

const Session = ({ isLoggedIn, isUnicorn }) => {  if (isLoggedIn) {   return <SignOut />;  } else if (isUnicorn) {   return <UnicornLogin />;  };return <Login />;  };  

Using Ternary Operator

Also, less awful, yet prone to the same struggles as using if/else statements when more changes inevitably occur.

const Session = ({ isLoggedIn, isUnicorn }) => {  if (isLoggedIn) {   return <SignOut />;  }return isUnicorn ? <UnicornLogin /> : <Login />;  };  

Conditional Gotchas

Now that we've seen how to use conditional rendering in React, let's take a look at some specific examples where conditional rendering may not do what you expect.

Logical "&&" Operator

Rendering a 0 when mapping

When using "&&"to check the length of a data set and then mapping over it will render "0"when that list is empty.

This was recently highlighted by Kent C. Dodds in his article https://kentcdodds.com/blog/use-ternaries-rather-than-and-and-in-jsx

The code below will render "0" when data is empty.

const RenderData = ({ data }) => data.length && data.map(...);  

This can be resolved by either using a ternary operator instead of "&&".

const RenderData = ({ data }) => data.length > 0 ? data.map(...) : null;  

This can also be resolved by either using an if/else statement.

const RenderData = ({ data }) => data.length > 0 ? data.map(.const RenderData = ({ data }) => {  if (data.length === 0) return null;return data.map(...)  }  

Rendering a 0 in a component

This React Native specific, but when conditionally rendering a component and passing in your condition you may inadvertently render a 0. This results in your app crashing and the following error message:"Invariant Violation: Text strings must be rendered within a component.".

This will crash your app if "message" is ever 0:

message && <Text>{message}</Text>  

Nested Ternaries

Ternaries are nice if you have one condition. However, it is too easy to not refactor and quickly add another check and then another.

This is a simple example, you can imagine what this would look like if each component we rendered were 5-10 or more lines long.

const RenderData = ({ data }) => {  return data.length === 0 ? null   : data.length === 1   ? <SingleItem data={data} />   : data.length === 2   ? <DoubleItem data={data} />   : <MultiItem data={data} />  }  

Writing Better Conditions

We've taken a look at how to write basic conditional statements in React, along with some pitfalls to avoid. Let's consider how we can write better conditional code in React.

Conditional Operator Component

I think it is easier to read JSX if your brain only has to parse and not conditional statements plus . So, how can we write conditional operators as XML?

Let's consider creating a component called "RenderIf" and takes a boolean property of "isTrue" and renders its children.

export const RenderIf = ({ children, isTrue }) => isTrue ? children : null;RenderIf.propTypes = {  children: node.isRequired,  isTrue: bool.isRequired,  };  

Re-writing our example with the "RenderIf" component, I'm mostly looking at XML. However, there is still some boolean logic that could be cleaned up.

const RenderData = ({ data }) => {  return (   <>    <RenderIf isTrue={data.length === 1}>     <SingleItem data={data} />    </RenderIf>    <RenderIf isTrue={data.length === 2}>     <DoubleItem data={data} />    </RenderIf>    <RenderIf isTrue={data.length > 2}>     <MultiItem data={data} />    </RenderIf>   </>  );  }  

We can clean up the boolean logic by wrapping our "RenderIf" component.

const IfSingleItem = ({ children, data }) => <RenderIf isTrue={data.length === 1}>{children}</RenderIf>  const IfDoubleItem = ({ children, data }) => <RenderIf isTrue={data.length === 2}>{children}</RenderIf>  const IfMultiItem = ({ children, data }) => <RenderIf isTrue={data.length > 3}>{children}</RenderIf>const RenderData = ({ data }) => {  return (   <>    <IfSingleItem data={data}>     <SingleItem data={data} />    </IfSingleItem>    <IfDoubleItem data={data}>     <DoubleItem data={data} />    </IfDoubleItem>    <IfMultiItem data={data}>     <MultiItem data={data} />    </IfMultiItem>   </>  );  }  

We could refactor this even more, but this is good enough for now.

When to Refactor

Often times if there is an accumulation of complexity in a component it is a sign that there are components that should be refactored out. Although knowing exactly when and how to refactor is hard to know, here are some general rules of thumb that you might consider.

100+ Lines of Code

Keep components to less than 100 lines. As you start to get into the 100-250 line territory you should really start thinking about refactoring. If you are at 500+ lines of code, that should be refactored as soon as possible.

High Cyclomatic Complexity

Cyclomatic complexity is the number of paths through your code. So, if you have a simple if/else block, then it has a cyclomatic complexity of 2, where as if you had a block of if/else if/else if/else if/else, the cyclomatic complexity would be 5.

You can enforce this by using the ESLint complexity rule

It is up to you what level of complexity is appropriate, but somewhere around 4-5 is usually a good place to start.

Cleaner React

We can write cleaner React by extracting out distracting syntax and knowing when to refactor.

Creating a helper component like "RenderIf" is an example in how you could extract out conditional logic into a declarative syntax. This makes it a little bit easier for your brain since it is mostly taking in XML. Building on that idea, we can wrap our helper component to create a richer set of conditional components that add even more context.

At the end of the day, a component that is large and complex, no matter how clean the React is, will be prone to bugs and simply not fun to work on. It is a good practice to know when to refactor and to be disciplined to do that refactor when you know it needs to happen.

Happy coding and keep your React clean!

Originally posted on ZEAL's blog here