Rendering Elements

Question 1

What is the smallest building block of a React app?

Answer 1

Element

Question 2

Unlike browser DOM elements, React elements are plain ______?

Answer 2

Objects! They are cheap to create and React DOM takes care of updating the DOM to match the React elements.

Question 3

What is the name of the DOM node where everything inside it will be managed by React DOM?

Answer 3

Root.

Question 4

Can you have more than one root DOM node?

Answer 4

Applications built with just React usually have a single root DOM node.

However, ff you are integrating React into an existing app, you may have as many isolated root DOM nodes as you like.

Question 5

What is the ReactDOM method used to render an element to the page?

Answer 5

ReactDOM.render()

Question 6

True/False? React elements are immutable

Answer 6

True. Once you create an element, you can’t change its children or attributes. An element is like a single frame in a movie: it represents the UI at a certain point in time.

Question 7

Given the following example, when setInterval fires, what will be updated?

Answer 7

Only the time! React DOM compares the element and its children to the previous one, and only applies the DOM updates necessary to bring the DOM to the desired state.