Grammatical pattern for real numbers using XRegExp.build

real-xregexp.js

// Creating a grammatical pattern for real numbers using XRegExp.build

/*
 * Approach 1: Make all of the subpatterns reusable
 */

var lib = {
    digit:             /[0-9]/,
    exponentIndicator: /[Ee]/,
    digitSeparator:    /[_,]/,
    sign:              /[+-]/,
    point:             /[.]/
};
lib.preexponent = XRegExp.build('(?xn)\
    {{sign}} ?              \
    (?= {{digit}}           \
      | {{point}}           \
    )                       \
    ( {{digit}} {1,3}       \
      ( {{digitSeparator}} ?\
        {{digit}} {3}       \
      ) *                   \
    ) ?                     \
    ( {{point}}             \
      {{digit}} +           \
    ) ?                     ',
    lib
);
lib.exponent = XRegExp.build('(?x)\
    {{exponentIndicator}}\
    {{sign}} ?           \
    {{digit}} +          ',
    lib
);
lib.real = XRegExp.build('(?x)\
    ^              \
    {{preexponent}}\
    {{exponent}} ? \
    $              ',
    lib
);

/*
 * Approach 2: No need to reuse the subpatterns. {{sign}} and {{digit}} are defined twice, but that
 * can be avoided by defining them before constructing the main pattern (see Approach 1).
 */

var real = XRegExp.build('(?x)\
    ^              \
    {{preexponent}}\
    {{exponent}} ? \
    $              ',
    {
        preexponent: XRegExp.build('(?xn)\
            {{sign}} ?              \
            (?= {{digit}}           \
              | {{point}}           \
            )                       \
            ( {{digit}} {1,3}       \
              ( {{digitSeparator}} ?\
                {{digit}} {3}       \
              ) *                   \
            ) ?                     \
            ( {{point}}             \
              {{digit}} +           \
            ) ?                     ',
            {
                sign:           /[+-]/,
                digit:          /[0-9]/,
                digitSeparator: /[_,]/,
                point:          /[.]/
            }
        ),
        exponent: XRegExp.build('(?x)\
            {{exponentIndicator}}\
            {{sign}} ?           \
            {{digit}} +          ',
            {
                sign:              /[+-]/,
                digit:             /[0-9]/,
                exponentIndicator: /[Ee]/
            }
        )
    }
);

/*
 * Matches:
 * -0
 * 1,000
 * 10_000_000
 * 1,111.1111
 * 01.0
 * .1
 * 1e2
 * +1.1e-2
 *
 * Doesn't match:
 * ,100
 * 10,00
 * 1,0000
 * 1.
 * 1.1,111
 * 1k
 */

This is used in my blog post Creating Grammatical Regexes Using XRegExp.build.