How to use the word/styles.xml function in word

public async extract(data: Buffer): Promise {
        const zipContent = await JSZip.loadAsync(data);

        const stylesContent = await zipContent.files["word/styles.xml"].async("text");
        const stylesFactory = new ExternalStylesFactory();
        const styles = stylesFactory.newInstance(stylesContent);

        const documentContent = zipContent.files["word/document.xml"];
        const documentRefs: IDocumentRefs = this.extractDocumentRefs(await documentContent.async("text"));
        const titlePageIsDefined = this.titlePageIsDefined(await documentContent.async("text"));

        const relationshipContent = zipContent.files["word/_rels/document.xml.rels"];
        const documentRelationships: IRelationshipFileInfo[] = this.findReferenceFiles(await relationshipContent.async("text"));

        const media = new Media();

        const headers: IDocumentHeader[] = [];
        for (const headerRef of documentRefs.headers) {
            const relationFileInfo = documentRelationships.find((rel) => rel.id === headerRef.id);
            if (relationFileInfo === null || !relationFileInfo) {

.then((content) => {
        this.docx = new Docx(content);
        return this.asyncResult.files['word/styles.xml'].async('string');
      })
      .then((content) => {

parseStylesAsync(zip) {
            return zip.files["word/styles.xml"]
                .async("string")
                .then((xml) => this.parseStylesFile(xml));
        }