useMemo - useCallBack

function Button({ color, children }) {
  const textColor = useMemo(    () => slowlyCalculateTextColor(color),    [color] // ✅ Don’t recalculate until `color` changes  );  return (
    <button className={'Button-' + color + ' Button-text-' + textColor}>
      {children}
    </button>
  );
}

const memoizedCallback = useCallback(
  () => {
    doSomething(a, b);
  },
  [a, b],
);
const memoizedValue = useMemo(() => computeExpensiveValue(a, b), [a, b]);
useCallback(fn, deps) is equivalent to useMemo(() => fn, deps).

Comments

for loop in javascript - promise - .eslintrc for "for of"

the vast majority of cases map , forEach , find etc. can be used. async function printFiles () { const files = await getFilePaths(); await Promise.all(files. map (async (file) => { const contents = await fs.readFile(file, 'utf8') console.log(contents) })); } const inventory = [ { name : 'apples' , quantity : 2 } , { name : 'bananas' , quantity : 0 } , { name : 'cherries' , quantity : 5 } ] ; const result = inventory . find ( ( { name } ) => name === 'cherries' ) ; function getFirstMatching(array) { for (let item of array) { const result = heavyTransform(item); if (result) { return result; } } } Specifically this shuts down the whole no-restricted-syntax. If you want to cherry-pick, here is the current definition: 'no-restricted-syntax' : [ 'error' , { selector : 'ForInStatement' , message...

Apollo client - cache APIs - auto update cache - erase cache - reactive variables - deletion - addition

Apollo Client 3 Local only fields Reactive Variables const cache = new InMemoryCache ( { typePolicies : { Todo : { // If one of the keyFields is an object with fields of its own, you can // include those nested keyFields by using a nested array of strings: keyFields : [ "date" , "user" , [ "email" ] ] , } } , } ) ; This internal data is intended to be easily JSON-serializable , so you can take a snapshot with cache.extract() , save it somewhere, and later restore with cache.restore(snapshot) . Here’s a mutation called EditTodo that returns the new todo value in the mutation response. mutation EditTodo ( $id : Int ! , $text : String ! ) { editTodo ( id : $id , text : $text ) { success todo { # <- Returning it here id text completed } error { ... on TodoNotFoundError { message } ... on TodoValidationE...

window.URL.createObjectURL is not (yet) available in jest-dom - testing scenario

Since window.URL.createObjectURL is not (yet) available in jest-dom, you need to provide a mock implementation for it. Don't forget to reset the mock implementation after each test. describe ( "your test suite" , () => { window . URL . createObjectURL = jest . fn (); afterEach (() => { window . URL . createObjectURL . mockReset (); }); it ( "your test case" , () => { expect ( true ). toBeTruthy (); }); });

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