Multiline Regular Expressions using ES6 Template Strings

multiline-regexp.js

/**
 * Inspired by XRegExp via 2ality
 * http://www.2ality.com/2012/12/template-strings-xregexp.html
 * http://xregexp.com/
 */

import test from 'ava';

export function rx(flags) {
    const trailingComments = /\s+#.*$/gm;
    const surroundingWhitespace = /^\s+|\s+$/gm;
    const literalNewlines = /[\r\n]/g;

    return (strings, ...values) => {
        function toPattern(pattern, rawString, i) {
            var value = values[i];

            if (value == null) {
                return pattern + rawString;
            }

            if (value instanceof RegExp) {
                value = value.source;
            }

            return pattern + rawString + value;
        }

        const compiledPattern = strings.raw
            .reduce(toPattern, '')
            .replace(trailingComments, '')
            .replace(surroundingWhitespace, '')
            .replace(literalNewlines, '');

        return new RegExp(compiledPattern, flags);
    };
}

test('should compile a multiline RegExp', async assert => {
    // flags on partials are ignored
    const open = /\/\*\*/g;
    const close = /\*\//m;

    const expression = rx('gm')`
        # Match a non-recursive block comment
        (
            # Must be first thing on a line
            ^[\t ]*
            ${open} # Trailing comment
            (
                # Match any character including newlines (non-greedy)
                [\s\S]*?
            )
            ${close}
        )
        # Grab trailing newlines and discard them
        [\r\n]*
    `;

    assert.same(expression, /(^[\t ]*\/\*\*([\s\S]*?)\*\/)[\r\n]*/gm);
});