regular-expression-builder.js

    var template = "(a{1,3})12(?:b|3)(\\d*?)(\\d+)";

    var rb = new reBuilder();
    rb.build(
        rb.capture(
            rb.repeat(1, 3, true, 'a') // third parameter is isGreedy
        ),
        '12',
        rb.repeat(0, 1, true,
            rb.or(
                'b',
                '3'
            )
        ),
        rb.capture(
            rb.repeat(0, Infinity, false,
                rb.charDigit()
            )
        ),
        rb.named(
            'digits',
            rb.repeat(1, Infinity, true,
                rb.charDigit()
            )
        )
    );
    var re = rb.generate();