react-hooks

问题 I am trying to get the text value from a dropdown select using [useState} in React Hooks. I just get the value (number) rather than the text. Ive copied the bits of code below which control the select dropdown. What am i missing here? Thanks. const [addrtype, setAddrType] = useState('Home') function handleAddrTypeChange(e) { setAddrType(e.target.value); console.log(addrtype) } <select defaultValue={addrtype} onChange={handleAddrTypeChange} className="browser-default custom-select"> <option

问题 I am trying to get the text value from a dropdown select using [useState} in React Hooks. I just get the value (number) rather than the text. Ive copied the bits of code below which control the select dropdown. What am i missing here? Thanks. const [addrtype, setAddrType] = useState('Home') function handleAddrTypeChange(e) { setAddrType(e.target.value); console.log(addrtype) } <select defaultValue={addrtype} onChange={handleAddrTypeChange} className="browser-default custom-select"> <option

问题 I'm learning Error Boundaries in React. I think I've got a good basic understanding but am having trouble implementing them for asynchronous processes, such as loading data. Let's say I have a simple component that, using React hooks, loads some data from a remote API. Since error boundaries won't work using asynchronous processes per se, instead of throwing an error in catch , this component stores the error in state and throws it on next re-render // MovieDb.js import axios from "axios"

问题 I'm learning Error Boundaries in React. I think I've got a good basic understanding but am having trouble implementing them for asynchronous processes, such as loading data. Let's say I have a simple component that, using React hooks, loads some data from a remote API. Since error boundaries won't work using asynchronous processes per se, instead of throwing an error in catch , this component stores the error in state and throws it on next re-render // MovieDb.js import axios from "axios"

问题 I have set up an effect inside my component, which changes the view if another state attribute changes. But for some reason, when the component mounts, the effect is run, even though the value of detailIndex has not changed. const EventsSearchList = () => { const [view, setView] = useState('table'); const [detailIndex, setDetailIndex] = useState(null); useEffect(() => { console.log('onMount', detailIndex); // On mount shows "null" }, []); useEffect( a => { console.log('Running effect',

问题 What is the main difference between useCallback,useMemo and useEffect. ?.Give examples of when to use useCallback,useMemo and useEffect. 回答1: A short explanation. useEffect It's the alternative for the class component lifecycle methods componentDidMount , componentWillUnmount , componentDidUpdate , etc. You can also use it to create a side effect when dependencies change, i.e. "If some variable changes, do this". useCallback On every render, everything that's inside a functional component

问题 What is the main difference between useCallback,useMemo and useEffect. ?.Give examples of when to use useCallback,useMemo and useEffect. 回答1: A short explanation. useEffect It's the alternative for the class component lifecycle methods componentDidMount , componentWillUnmount , componentDidUpdate , etc. You can also use it to create a side effect when dependencies change, i.e. "If some variable changes, do this". useCallback On every render, everything that's inside a functional component

问题 What is the main difference between useCallback,useMemo and useEffect. ?.Give examples of when to use useCallback,useMemo and useEffect. 回答1: A short explanation. useEffect It's the alternative for the class component lifecycle methods componentDidMount , componentWillUnmount , componentDidUpdate , etc. You can also use it to create a side effect when dependencies change, i.e. "If some variable changes, do this". useCallback On every render, everything that's inside a functional component

问题 i'm Trying to make react paypal button that changes the billing amount on props change. I call the following component with props price and everytime the price change i would like to rerender the button to update the actual price. const PaypalForm = props => { let paypalRef = useRef(); useEffect(() => { window.paypal .Buttons({ createOrder: (data, actions) => { return actions.order.create({ purchase_units: [ { description: "test", amount: { currency_code: "USD", value: props.price } } ] }); }

问题 i'm Trying to make react paypal button that changes the billing amount on props change. I call the following component with props price and everytime the price change i would like to rerender the button to update the actual price. const PaypalForm = props => { let paypalRef = useRef(); useEffect(() => { window.paypal .Buttons({ createOrder: (data, actions) => { return actions.order.create({ purchase_units: [ { description: "test", amount: { currency_code: "USD", value: props.price } } ] }); }