Is conditionally rendering a React component instead of raw markup save performance?

Question

This is something that makes sense in my head but I haven't been able to find any facts/articles to back this up.

Essentially is doing something like

render() {
  return (
    someBoolean && <div>Some Markup</div>
  )
}

less performant than

render() {
  return (
    someBoolean && <SomeComponent />
  )
}

where SomeComponent has the same exact markup as the previous example.

My reasoning is since the markup will have to be created on every re-render it'll take up more memory whereas the saved component SomeComponent will be referenced in memory and won't have to be created on every re-render.

Is there somewhere in the react docs that explains this more thoroughly?
Or is this reasoning not accurate?

Answer 1

JSX is syntactic sugar for React.createElement. As it can be seen in Babel REPL, they are

return someBoolean && React.createElement(
  "div",
  null,
  "Some Markup"
);

and

return someBoolean && React.createElement(SomeComponent, null);

respectively.

When someBoolean is falsy, React.createElement isn't called and render becomes no-op.

SomeComponent isn't cached, it is re-created every time. In comparison with raw markup, it provides negligible overhead, considering that it is a stateless component:

const SomeComponent = () => <div>Some Markup</div>;

Both options are very fast and aren't supposed to be optimized.

Answer 2

Whether it's conditional or not is not an issue, as neither will be evaluated past the && if someBoolean is false.

The real question is whether a defined React subcomponent has a performance advantage or penalty versus plain JSX markup defined within another component. For practical purposes, there is no performance difference unless you are making use of custom functions for lifecycle hooks.

For example, if you use a subcomponent, you may define a separate shouldComponentUpdate method within that component and thereby decouple its updates from the parent. In the case of plain JSX, it will update as part of the parent component.