kjelsrud.dev/node_modules/mdast-util-to-markdown/lib/util/pattern-compile.js

/**
 * @typedef {import('../types.js').Unsafe} Unsafe
 */

/**
 * @param {Unsafe} pattern
 * @returns {RegExp}
 */
export function patternCompile(pattern) {
  if (!pattern._compiled) {
    const before =
      (pattern.atBreak ? '[\\r\\n][\\t ]*' : '') +
      (pattern.before ? '(?:' + pattern.before + ')' : '')

    pattern._compiled = new RegExp(
      (before ? '(' + before + ')' : '') +
        (/[|\\{}()[\]^$+*?.-]/.test(pattern.character) ? '\\' : '') +
        pattern.character +
        (pattern.after ? '(?:' + pattern.after + ')' : ''),
      'g'
    )
  }

  return pattern._compiled
}