React Render Must Not Have Side Effects

React render() Quiz

render() is the only required method in a React component.


render() can only return elements, not other React components.


render() must be a pure function.


Which of the following JSX values is invalid?

return (<div>I'm element one</div><div>I'm element two</div>);
return (<div><div>I'm element one</div><div>I'm element two</div></div>);

It's okay if render() sometimes returns a different result when given the same input.


Which of the following expressions is definitely not a side effect?

const fullName = this.props.firstName + ' ' + this.props.lastName;
const id = Math.random() * 99;


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