A tagged template string implementation for composing regexes

regex-tagged-template-string.ts

import { isRegExp, zipWith } from 'lodash';

export function regex(strings: TemplateStringsArray, ...values: any[]): RegExp {
  const pattern = zipWith(strings, values, (str, value) => {
    if (isRegExp(value)) {
      value = value.source.replace(/^\^|\$$/g, '');
    }

    return str + (value ?? '');
  }).join('');

  return new RegExp(pattern);
}

const MIME_TYPE = /^[a-zA-Z]+\/[a-zA-Z]+$/;

/**
 * Matches the beginning of a base64 string
 *
 * For performance reasons, this regex is not exhaustive. It only validates the beginning of the string.
 *
 * A prior version of this regex attempted to validate the entire string, but it had terrible peformance, and could cause out-of-memory errors.
 */
const BASE64_STRING = /^[A-Za-z\d+/_-]{1,100}/;

/**
 * Matches the beginning of a well-formed, base64-encoded data url
 *
 * For performance reasons, this regex is not exhaustive. It only validates the beginning of the string.
 *
 * A prior version of this regex attempted to validate the entire string, but it had terrible peformance, and could cause out-of-memory errors.
 */
const DATA_URL = regex`^data:${MIME_TYPE};base64,${BASE64_STRING}`;