Calling Hooks properly

#javascript #react #beginners

We should always use hooks at the top level of our react application, before any early returns in order to prevent hooks being called every re-render and only be called when necessary. That`s what allows react to correctly preserve the state of Hooks between multiple useState and useEffect calls.

Noncompliant example

function Test() {
const [testCount, setTestCount] = useState(0);
if (testCount !== 0) {
useEffect(function() { // Noncompliant, this Hook is called conditionally
localStorage.setItem('testData', testCount);
});
}

return

{ getName() }
};

function getName() {
const [name] = useState('John'); // Noncompliant, this Hook is called from simple JavaScript function
return name;
};

Compliant solution

`
function Test() {
const [testCount, setTestCount] = useState(0);
useEffect(function() {
if (testCount !== 0) {
localStorage.setItem('testData', testCount);
}
});

const [name] = useState('John');
return

{ name }
};
`

This way we are not putting any hooks inside if statements and we can prevent it from suffering any unwanted render.

Hope someone found it useFull

Lautaro