var example = '9_000_000_000'
var example2 = '9_000_000_000xx'
var regex1 = /^(?:\d(?:_?\d)*)?\.?\d(?:_?\d)*(?:e[+-]?\d(?:_?\d)*)?/
var regex2 = /^(?:\d+(?:_?\d+)*)?\.?\d+(?:_?\d+)*(?:e[+-]?\d(?:_?\d)*)?/
var regex3 = /\d+(?:_?\d+)*n/example.match(regex1)
example2.match(regex1)example.match(regex2)
example2.match(regex2)example.match(regex3)
example2.match(regex3)