Context

The context holds the book and the state of the reader that the rest of the engine builds on. The manifest is fixed for the lifetime of the reader; everything else is runtime state.

type ContextState = {
  manifest: Manifest
  /**
   * The container the reader is mounted into. Undefined until `mount()`.
   */
  rootElement?: HTMLElement
  /**
   * Whether a loaded document uses vertical writing. Undefined until one
   * has been detected.
   */
  hasVerticalWriting?: boolean
  /**
   * The rendition layout from the manifest, `reflowable` when it has none.
   */
  assumedRenditionLayout: "reflowable" | "pre-paginated"
  /**
   * Cover the case where either renditionLayout is pre-paginated
   * or if we detect all the pages being pre-paginated. This value
   * can be useful to detect a comics or manga type book. It uses
   * the manifest as well but offer more convenience.
   */
  isFullyPrePaginated: boolean
  /**
   * Whether the book can be shown in a spread at all. It cannot when its
   * `rendition:spread` is `none` or its `rendition:flow` is
   * `scrolled-continuous`, and the `spreadMode` setting then changes nothing.
   */
  isSpreadAllowed: boolean
}

Read a value with reader.context.value, or follow it with reader.context.watch(key), which emits the current value as soon as you subscribe and again whenever it changes.

Whether two pages are shown side by side is not part of the context: the viewport decides it with its size, within what isSpreadAllowed permits. See Spread mode.