Render based on state (rather than directly DOM manipulate)

[oliverjam]

week10-AJ/src/components/play.js

Lines 21 to 28 in 4888b86

	<button onClick={(event) => {
	if (event.target.className === "user-card hidden"){
	event.target.classList.remove("hidden");
	event.target.classList.add("flipped");
	} else{
	event.target.parentNode.classList.remove("hidden");
	event.target.parentNode.classList.add("flipped");
	}

This is kind of a subtle React philosophy thing, but you should generally be suspicious if your code ever has to touch the real DOM. React is designed to handle all DOM updates for you, so if you're ever doing a querySelector or directly changing classNames etc that's usually something to avoid.

Remember your component re-runs whenever state changes, which means you can put conditions and dynamic stuff into your JSX to determine e.g. what classNames elements should have. You just need to have state values that let you know what to render.

E.g. if you kept track of the selected cards in state you could then declaratively render your UI based on that state:

const [selectedCards, setSelectedCards] = React.useState([]);

{data.map(user => (
  <button
    className={selectedCards.includes(user) ? "flipped" : "hidden"}
    onClick={() => putUserIntoSelectedCardsSomehow(user)}
  >
  {user}
  </button>
)}

Generally React updates are a lot easier to manage if you do as little logic as possible in event handlers and try to just make them simple state updates. You can then use the updated state in your render to determine what the page should look like.