src/service/document-state.js
/**
   * Returns the value of "document.hidden" property. The reasons why it may
   * not be visible include document in a non-active tab or when the document
   * is being pre-rendered via link with rel="prerender".
   * @return {boolean}
   */
Returns the value of "document.hidden" property. The reasons why it may
not be visible include document in a non-active tab or when the document
is being pre-rendered via link with rel="prerender".
@return {boolean}
Returns the value of " document . hidden " property . The reasons why it may not be visible include document in a non - active tab or when the document is being pre - rendered via link with rel = " prerender " . @return { boolean }
isHidden() {
    if (!this.hiddenProp_) {
      return false;
    }
    return this.document_[this.hiddenProp_];
  }
isHidden ( ) { if ( ! this . hiddenProp_ ) { return false ; } return this . document_ [ this . hiddenProp_ ] ; }
Returns the value of "document.hidden" property.
Returns the value of " document . hidden " property .