node_modules/@reduxjs/toolkit/src/query/utils/joinUrls.ts

import { isAbsoluteUrl } from './isAbsoluteUrl'

const withoutTrailingSlash = (url: string) => url.replace(/\/$/, '')
const withoutLeadingSlash = (url: string) => url.replace(/^\//, '')

export function joinUrls(
  base: string | undefined,
  url: string | undefined,
): string {
  if (!base) {
    return url!
  }
  if (!url) {
    return base
  }

  if (isAbsoluteUrl(url)) {
    return url
  }

  const delimiter = base.endsWith('/') || !url.startsWith('?') ? '/' : ''
  base = withoutTrailingSlash(base)
  url = withoutLeadingSlash(url)

  return `${base}${delimiter}${url}`
}