const copyText = async (text) => await navigator.clipboard.writeText(text)
copyText('单行代码 前端世界')   

const getSelectedText = () => window.getSelection().toString();
getSelectedText();

const dayDiff = (date1, date2) => Math.ceil(Math.abs(date1.getTime() - date2.getTime()) / 86400000);

dayDiff(new Date("2021-10-21"), new Date("2022-02-12"))
// Result: 114

const average = (arr) => arr.reduce((a, b) => a + b) / arr.length;
average([1,9,18,36]) //16