let test = 'hello world'
// 后行断言
let res = test.match(/hello(?=\sworld)/)
console.log(res)
// 先行断言
res = test.match(/(?<=hello\s)world/)
console.log(res)
let test = 'hello world'
// 后行断言
let res = test.match(/hello(?=\sworld)/)
console.log(res)
// 先行断言
res = test.match(/(?<=hello\s)world/)
console.log(res)