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Disallow problematic leaked values from being rendered (inferno/jsx-no-leaked-render)

🔧 This rule is automatically fixable by the --fix CLI option.

Using the && operator to render some element conditionally in JSX can cause unexpected values being rendered, or even crashing the rendering.

Rule Details

This rule aims to prevent dangerous leaked values from being rendered since they can cause unexpected values reaching the final DOM or even crashing your render method.

In Inferno, you might end up rendering unexpected values like 0 or NaN. In React Native, your render method will even crash if you render these values:

const Example = () => {
  return (
    <>
      {0 && <Something />}
      {/* Inferno: renders undesired 0 */}
      {/* Inferno Native: crashes 💥 */}

      {NaN && <Something />}
      {/* Inferno: renders undesired NaN */}
      {/* Inferno Native: crashes 💥 */}

      {'' && <Something />}
      {/* Inferno: renders nothing */}
      {/* Inferno Native, with Inferno < 18: crashes 💥 */}
    </>
  )
}

This can be avoided by:

  • coercing the conditional to a boolean: {!!someValue && <Something />}
  • transforming the binary expression into a ternary expression which returns null for falsy values: {someValue ? <Something /> : null}

This rule is autofixable; check the Options section to read more about the different strategies available.

Examples of incorrect code for this rule:

const Component = ({ count, title }) => {
  return <div>{count && title}</div>
}
const Component = ({ count }) => {
  return <div>{count && <span>There are {count} results</span>}</div>
}
const Component = ({ elements }) => {
  return <div>{elements.length && <List elements={elements} />}</div>
}
const Component = ({ nestedCollection }) => {
  return (
    <div>
      {nestedCollection.elements.length && <List elements={nestedCollection.elements} />}
    </div>
  )
}
const Component = ({ elements }) => {
  return <div>{elements[0] && <List elements={elements} />}</div>
}
const Component = ({ numberA, numberB }) => {
  return <div>{(numberA || numberB) && <Results>{numberA + numberB}</Results>}</div>
}
// If the condition is a boolean value, this rule will report the logical expression
// since it can't infer the type of the condition.
const Component = ({ someBool }) => {
  return <div>{someBool && <Results>{numberA + numberB}</Results>}</div>
}

Examples of correct code for this rule:

const Component = ({ elements }) => {
  return <div>{elements}</div>
}
// An OR condition it's considered valid since it's assumed as a way
// to render some fallback if the first value is falsy, not to render something conditionally.
const Component = ({ customTitle }) => {
  return <div>{customTitle || defaultTitle}</div>
}
const Component = ({ elements }) => {
  return <div>There are {elements.length} elements</div>
}
const Component = ({ elements, count }) => {
  return <div>{!count && 'No results found'}</div>
}
const Component = ({ elements }) => {
  return <div>{!!elements.length && <List elements={elements} />}</div>
}
const Component = ({ elements }) => {
  return <div>{Boolean(elements.length) && <List elements={elements} />}</div>
}
const Component = ({ elements }) => {
  return <div>{elements.length > 0 && <List elements={elements} />}</div>
}
const Component = ({ elements }) => {
  return <div>{elements.length ? <List elements={elements} /> : null}</div>
}
const Component = ({ elements }) => {
  return <div>{elements.length ? <List elements={elements} /> : <EmptyList />}</div>
}

Rule Options

The supported options are:

validStrategies

An array containing "coerce", "ternary", or both (default: ["ternary", "coerce"]) - Decide which strategies are considered valid to prevent leaked renders (at least 1 is required). The "coerce" option will transform the conditional of the JSX expression to a boolean. The "ternary" option transforms the binary expression into a ternary expression returning null for falsy values. The first option from the array will be the strategy used when autofixing, so the order of the values matters.

It can be set like:

{
  // ...
  "inferno/jsx-no-leaked-render": [<enabled>, { "validStrategies": ["ternary", "coerce"] }]
  // ...
}

Assuming the following options: { "validStrategies": ["ternary"] }

Examples of incorrect code for this rule, with the above configuration:

const Component = ({ count, title }) => {
  return <div>{count && title}</div>
}
const Component = ({ count, title }) => {
  return <div>{!!count && title}</div>
}

Examples of correct code for this rule, with the above configuration:

const Component = ({ count, title }) => {
  return <div>{count ? title : null}</div>
}
const Component = ({ count, title, empty }) => {
  return <div>{count ? title : empty}</div>
}

Assuming the following options: { "validStrategies": ["coerce"] }

Examples of incorrect code for this rule, with the above configuration:

const Component = ({ count, title }) => {
  return <div>{count && title}</div>
}
const Component = ({ count, title }) => {
  return <div>{count ? title : null}</div>
}

Examples of correct code for this rule, with the above configuration:

const Component = ({ count, title }) => {
  return <div>{!!count && title}</div>
}
const Component = ({ count, title, empty }) => {
  return <div>{count ? title : empty}</div>
}

When Not To Use It

If you are working in a typed-codebase which encourages you to always use boolean conditions, this rule can be disabled.

Further Reading