es9 正则扩展提取url

 let str = '<a href="http://www.baidu.com">测试数据</a>';

  const reg = /<a href="(?<url>.*)">(?<text>.*)<\/a>/

  const result = reg.exec(str)

  console.log(result,"sjsjjs")

1.正向断言：

  let str = 'jjjjjjdddd测试数据6666哈哈哈哈'

  const reg = /\d+(?=哈)/;

  const result = reg.exec(str)

  console.log(result,"djjdjdjdj")

2.反向断言
  let str = 'jjjjjjdddd测试数据6666哈哈哈哈'

  const reg = /(?<=据)\d+/

  const result = reg.exec(str)

  console.log(result,"djjdjdjdj")