next.js/packages/next/src/shared/lib/router/utils/is-dynamic.ts

import {
  extractInterceptionRouteInformation,
  isInterceptionRouteAppPath,
} from './interception-routes'

// Identify /.*[param].*/ in route string
const TEST_ROUTE = /\/[^/]*\[[^/]+\][^/]*(?=\/|$)/

// Identify /[param]/ in route string
const TEST_STRICT_ROUTE = /\/\[[^/]+\](?=\/|$)/

/**
 * Check if a route is dynamic.
 *
 * @param route - The route to check.
 * @param strict - Whether to use strict mode which prohibits segments with prefixes/suffixes (default: true).
 * @returns Whether the route is dynamic.
 */
export function isDynamicRoute(route: string, strict: boolean = true): boolean {
  if (isInterceptionRouteAppPath(route)) {
    route = extractInterceptionRouteInformation(route).interceptedRoute
  }

  if (strict) {
    return TEST_STRICT_ROUTE.test(route)
  }

  return TEST_ROUTE.test(route)
}