Example code 5 of Web Word(2).js

/**
 * Insert paragraphs to body at first
 * @param {HTMLElement} pageBodyElement - page body element
 * @param {Array.<HTMLElement>} paragraphs - paragraph array
 */
_insertParagraphsToBodyAtFirst(pageBodyElement, paragraphs) {
    if (pageBodyElement.firstChild) {
        // merge split paragraphs before.
        paragraphs.slice().reverse().forEach(paragraph => {
            const splitParagraphId = paragraph.getAttribute(SPLIT_PARAGRAPH_ID);
            let appended = false;
            if (splitParagraphId) {
                const nextParagraph = pageBodyElement.querySelector(`[${SPLIT_PARAGRAPH_ID}="${splitParagraphId}"]`);
                if (nextParagraph) {
                    const {firstChild} = nextParagraph;
                    paragraph.childNodes.forEach(
                        node => nextParagraph.insertBefore(node, firstChild)
                    );
                    paragraph.parentElement.removeChild(paragraph);
                    appended = true;
                }
            }
            if (!appended) {
                pageBodyElement.insertBefore(paragraph, pageBodyElement.firstChild);
            }
        });
    } else {
        paragraphs.forEach(
            paragraph => pageBodyElement.appendChild(paragraph)
        );
    }
}