gistfile1.js

var wsp = '(\\u0020|\\u0009|\\u000D|\\u000A)';
var digit = '\\d';
var digit_sequence = '(' + digit + '+' + ')';
var sign = '[-+]';
var exponent = '[eE]' + sign + '?' + digit_sequence;

var fractional_constant = 
    '(' + 
      digit_sequence + '?' + '\\.' + digit_sequence + 
      '|' +
      digit_sequence + '\\.' +
    ')';

var floating_point_constant = 
    '(' + 
      fractional_constant + exponent + '?' + 
      '|' + 
      digit_sequence + exponent + 
    ')';

var integer_constant = digit_sequence;
var comma = ',';

var comma_wsp = 
    '(' + 
      '(' + wsp + '+' + comma + '?' + wsp + '*' + ')' + 
      '|' + 
      '(' + comma + wsp + '*' + ')' + 
    ')';

var number = 
    '(' + 
      sign + '?' + integer_constant + 
      '|' + 
      sign + '?' + floating_point_constant + 
    ')';

new RegExp('^'+number+'$').test('5e');