React Render Must Not Have Side Effects

React render() Quiz

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

True.
False.

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

True.
False.

render() must be a pure function.

True.
False.

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.

True.
False.

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

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

Resources

Unlock your future in tech
Learn to code.

Learn about Flatiron School's Mission

With a new take on education that falls somewhere between self-taught prodigy and four-year computer science degree, the Flatiron School promises to turn students with little programming experience into developers.

In the six months since the Manhattan coding school was acquired by WeWork, it has spawned locations in Washington, D.C., Brooklyn, and London. Now, WeWork is opening a fourth Flatiron School location, this time in Houston.

Adam Enbar, Flatiron School's cofounder, believes now is the time to grow. "How the world is changing has impacted working and learning in very similar ways. We think education fundamentally is about one thing: enabling people to pursue a better life."

Learn. Love. Code.
Students come to Flatiron School to change their lives. Join our driven community of career-changers and master the skills you need to become a software engineer or a data scientist.
Find Us