5:["$","div",null,{"children":[["$","style",null,{"children":"*{margin:0;padding:0}"}],["$","a",null,{"className":"return-article fixed top-1 right-2 z-50 text-sky-400 hover:text-sky-500","href":"/demos/20191118/react-useMemo.html","children":"回到样例"}],null,["$","style",null,{"dangerouslySetInnerHTML":{"__html":"#app {\r\n font-size: 30px;\r\n}\r\n#app button {\r\n font-size: 24px;\r\n}"}}],["$","div",null,{"dangerouslySetInnerHTML":{"__html":"

点击add1按钮，sum发生变化

\r\n

点击set now time按钮，sum固定不变

\r\n

sum只随着count变化，而跟其他的state无关

\r\n\r\n

"}}],["$","div",null,{"dangerouslySetInnerHTML":{"__html":"\r\n\r\n"}}],["$","script",null,{"type":"text/babel","dangerouslySetInnerHTML":{"__html":"const { useState, useEffect, useMemo } = React;\r\n\r\nconst Home = () => {\r\n const [count, setCount] = useState(0);\r\n const [nowtime, setNowtime] = useState(0);\r\n const sum = useMemo(() => ((1 + count) * count) / 2 + \" ,random: \" + Math.random(), [count]);\r\n\r\n return (\r\n <>\r\n

count: {count}

\r\n

sum: {sum}

\r\n

nowtime: {nowtime}

\r\n \r\n \r\n \r\n );\r\n};\r\nReactDOM.render(, document.getElementById(\"app\"));"}}],["$","script",null,{"dangerouslySetInnerHTML":{"__html":"window.addEventListener('load', function () {\n if (window.parent !== window) {\n // 在 iframe 中\n // 隐藏回到文章的按钮\n document.querySelector('.return-article').style.display = 'none';\n // 隐藏底部的声明\n document.querySelector('.common-footer').style.display = 'none';\n }\n});"}}]]}] d:[["$","meta","0",{"name":"viewport