Example code 7 of Web Word(2).js

/**
 * Layout a page and return next page number
 * @param {number} pageNumber - page number
 * @returns {Promise} promise
 */
_layoutPage(pageNumber = 1) {
    const promise = new Promise((resolve, reject) => {
        const pageIndex = pageNumber - 1;
        const totalPageCount = this.pageBodyElements.length;
        if (pageNumber > totalPageCount || pageNumber > 100) {
            reject(pageNumber + 1);
        }
        const pageBodyElement = this.pageBodyElements[pageIndex];
        const pageBodyBottom = this._getBottom(pageBodyElement);
        const exceedParagraph = this._findExceedParagraph(pageBodyElement, pageBodyBottom);
        const insertBodyParagraph = false;
        let allExceedParagraphs, nextPageBodyElement;
        if (exceedParagraph) {
            allExceedParagraphs = this._getExceedAllParagraphs(pageBodyElement, pageBodyBottom);
            if (pageNumber >= totalPageCount) {
                this._appendPage(insertBodyParagraph);
            }
            nextPageBodyElement = this.pageBodyElements[pageIndex + 1];
            this._insertParagraphsToBodyAtFirst(nextPageBodyElement, allExceedParagraphs);
        }
        resolve(pageNumber + 1);
    });
    return promise;
}