| /** |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance |
| * with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, |
| * software distributed under the License is distributed on an |
| * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| * KIND, either express or implied. See the License for the |
| * specific language governing permissions and limitations |
| * under the License. |
| */ |
| |
| import { useEffect, useRef } from 'react'; |
| |
| /** |
| * Pass in a piece of state. |
| * This hook returns what the value of that state was in the previous render. |
| * Returns undefined (or whatever value you specify) the first time. |
| */ |
| export function usePrevious<T>(value: T): T | undefined; |
| export function usePrevious<T, INIT>(value: T, initialValue: INIT): T | INIT; |
| export function usePrevious<T>(value: T, initialValue?: any): T { |
| const previous = useRef<T>(initialValue); |
| useEffect(() => { |
| // useEffect runs after the render completes |
| previous.current = value; |
| }, [value]); |
| return previous.current; |
| } |