FAQ: The State Hook - Initialize State

Frequently Asked Questions React.js FAQ
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This community-built FAQ covers the “Initialize State” exercise from the lesson “The State Hook”.

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This exercise can be found in the following Codecademy content:

Learn React

FAQs on the exercise Initialize State

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{colorNames.map((colorName)=>(

    <button 

      onClick={() => setColor(colorName)} 

      key={colorName}>

         {colorName}

    </button>

))}

Why is a parentheses used and not curly braces for the arrow function (bolded) here?

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Hi @venky3434
welcome to the forums!
The first pair of parenthesis you highlighted which is wrapped around the variable colorName is the usual syntax for an arrow function: () => {}. Since it holds a single variable, the parenthesis aren’t necessary here. It could be written as colorName => {} as well.
The second pair of parenthesis which is wrapped around the html tags is JSX syntax. A multiple line JSX Expression must be wrapped in parenthesis. Javascript sees that as a single statement which means that you can use the short hand syntax for the arrow function and leave the curly braces.
See the docs here: Introducing JSX
Javascript Expressions are injected with curly braces in React.

4

I did not realize that the multiple line JSX expression would be seen as a single statement by JavaScript thus erasing the need for the curly braces. Thank you very much!

5

Is there a reason why in the initialize lesson the only way indicated to initialize a default value for a state variable is by passing it as a parameter to useState() instead of saying that it could also be used the traditional JS syntax for destructuring? :slight_smile:

//these are equivalent - output for toggle would be "Off"
const [toggle, setToggle] = useState("Off");
const [toggle = "Off", setToggle] = useState();
//if both present the latter prevails - output for toggle would be "On"
const [toggle = "Off", setToggle] = useState("On");