docusaurus/packages/docusaurus-utils-common/src/applyTrailingSlash.ts

/**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

import type {DocusaurusConfig} from '@docusaurus/types';

export type ApplyTrailingSlashParams = Pick<
  DocusaurusConfig,
  'trailingSlash' | 'baseUrl'
>;

// Trailing slash handling depends in some site configuration options
export default function applyTrailingSlash(
  path: string,
  options: ApplyTrailingSlashParams,
): string {
  const {trailingSlash, baseUrl} = options;

  if (path.startsWith('#')) {
    // Never apply trailing slash to an anchor link
    return path;
  }

  // TODO deduplicate: also present in @docusaurus/utils
  function addTrailingSlash(str: string): string {
    return str.endsWith('/') ? str : `${str}/`;
  }
  function removeTrailingSlash(str: string): string {
    return str.endsWith('/') ? str.slice(0, -1) : str;
  }
  function handleTrailingSlash(str: string, trailing: boolean): string {
    return trailing ? addTrailingSlash(str) : removeTrailingSlash(str);
  }

  // undefined = legacy retrocompatible behavior
  if (typeof trailingSlash === 'undefined') {
    return path;
  }

  // The trailing slash should be handled before the ?search#hash !
  const [pathname] = path.split(/[#?]/);

  // Never transform '/' to ''
  // Never remove the baseUrl trailing slash!
  // If baseUrl = /myBase/, we want to emit /myBase/index.html and not /myBase.html !
  // See https://github.com/facebook/docusaurus/issues/5077
  const shouldNotApply = pathname === '/' || pathname === baseUrl;

  const newPathname = shouldNotApply
    ? pathname
    : handleTrailingSlash(pathname, trailingSlash);

  return path.replace(pathname, newPathname);
}