Get useful browsing context information about a window.

determineBrowsingContext.js

function determineBrowsingContext(win = window) {
  /**
   * ---------------------------------------------------------------------------
   * The source browsing context of the specified window object or subframe.
   * ---------------------------------------------------------------------------
   * It can be a reference to the parent browsing context (for frames and other
   * embedded windows), or the opener browsing context (for windows opened from
   * another window).
   *
   * For windows opened from another window, it is possible not to have access
   * to the opener browsing context, depending on how the window was opened
   * (e.g link opened with `rel=noopener`). In such cases, the source browsing
   * context is `null`.
   */
  const $source = win.opener || (win.parent !== win && win.parent) || null;
  
  return Object.create(null, {
    $source: { value: $source },
    
    /**
     * -------------------------------------------------------------------------
     * Boolean value that indicates whether the specified window is embedded.
     * -------------------------------------------------------------------------
     * A window object is said to be "embedded" if it's a child browsing context
     * contained by an element within its source browsing context. This is `true`
     * for iframes, frames within a `<frameset>` element, etc.
     */
    embedded: { value: win.parent === $source },
    
    /**
     * -------------------------------------------------------------------------
     * Boolean value that indicates whether the specified window is standalone.
     * -------------------------------------------------------------------------
     * A window object is said to be "standalone" if no reference to a source
     * browsing context can be found for it, and if it is the topmost window in
     * its hierarchy of windows.
     */
    standalone: { value: !$source && win.top === win }
  });
}