‘useState’ is not defined no-undef React
You need to import “useState”: import React, { useEffect, useState } from “react”;
react-hooks
Reactjs separation of UI and business logic
Yes it is possible, That is called as Separation of concern. You can create your component structure as below. MyComponentDirectory – useCustomHook – Component – helper The code will look like this one. Hook const useCustomHook = () => { const [value, setValue] = useState(”); const handleClick = (value) => { setValue(value) //do something. }; … Read more
How to set initial state for useState Hook in jest and enzyme?
You can mock React.useState to return a different initial state in your tests: // Cache original functionality const realUseState = React.useState // Stub the initial state const stubInitialState = [‘stub data’] // Mock useState before rendering your component jest .spyOn(React, ‘useState’) .mockImplementationOnce(() => realUseState(stubInitialState)) Reference: https://dev.to/theactualgivens/testing-react-hook-state-changes-2oga
React Hook useEffect has a missing dependency: ‘dispatch’
UPDATE 09/11/2020 This solution is no longer needed on eslint-plugin-react-hooks@4.1.0 and above. Now useMemo and useCallback can safely receive referential types as dependencies.#19590 function MyComponent() { const foo = [‘a’, ‘b’, ‘c’]; // <== This array is reconstructed each render const normalizedFoo = useMemo(() => foo.map(expensiveMapper), [foo]); return <OtherComponent foo={normalizedFoo} /> } Here is another … Read more
React: useEffect vs useMemo vs useState
Your points are basically correct, some minor clarification: useState is causing a re-render on the call of the setState method (second element in the array returned). It does not have any dependencies like useMemo or useEffect. useMemo only recalculates a value if the elements in its dependency array change (if there are no dependencies – … Read more
Why need useRef and not mutable variable?
useRef will assign a reference for each component, while a variable defined outside a function component scope will only assigned once. useRef reference life span is component’s life span (it “dies” when the component unmounts, while JS variables are scope-blocked). Hence, define constant purpose variables outside of the component scope: // This statement will only … Read more
How to remove query param with react hooks?
For React Router V6 and above, see the answer below. Original Answer: Yes, you can use useHistory & useLocation hooks from react-router: import React, { useState, useEffect } from ‘react’ import { useHistory, useLocation } from ‘react-router-dom’ export default function Foo() { const [error, setError] = useState(”) const location = useLocation() const history = useHistory() … Read more
React – useState – why setTimeout function does not have latest state value?
This boils down to how closures work in JavaScript. The function given to setTimeout will get the flag variable from the initial render, since flag is not mutated. You could instead give a function as argument to toggleFlag. This function will get the correct flag value as argument, and what is returned from this function … Read more
useState hook setter incorrectly overwrites state
Welcome to the closure hell. This issue happens because whenever setState is called, state gets a new memory reference, but the functions changeValue1 and changeValue2, because of closure, keep the old initial state reference. A solution to ensure the setState from changeValue1 and changeValue2 gets the latest state is by using a callback (having the … Read more
Problems with debounce in useEffect
Every time your component re-renders, a new debounced verify function is created, which means that inside useEffect you are actually calling different functions which defeats the purpose of debouncing. It’s like you were doing something like this: const debounced1 = debounce(() => { console.log(state.username) }, 1000); debounced1(); const debounced2 = debounce(() => { console.log(state.username) }, … Read more