feat(package): modernize package metadata, typings, and test setup for ESM builds

ts/smartmarkdown.classes.mdparsedresult.ts

@@ -1,5 +1,16 @@
 import * as plugins from './smartmarkdown.plugins.js';
 
+export type TFrontmatterData = Record<string, unknown>;
+
+type TYamlNode = plugins.RootContent & {
+  type: 'yaml';
+  value: string;
+};
+
+const isYamlNode = (nodeArg: plugins.RootContent): nodeArg is TYamlNode => {
+  return nodeArg.type === 'yaml' && 'value' in nodeArg && typeof nodeArg.value === 'string';
+};
+
 export class MdParsedResult {
   public static async createFromMarkdownString(mdStringArg: string): Promise<MdParsedResult> {
     const mdParsedResult = new MdParsedResult();
@@ -7,24 +18,24 @@ export class MdParsedResult {
     return mdParsedResult;
   }
 
-  public originalString: string;
-  public title: string;
-  public html: string;
-  public frontmatterData: {[key: string]: any};
+  public originalString = '';
+  public title = '';
+  public html = '';
+  public frontmatterData: TFrontmatterData = {};
 
-  public async updateFromMarkdownString(mdStringArg: string) {
-    let yamlString: string;
+  public async updateFromMarkdownString(mdStringArg: string): Promise<void> {
+    this.originalString = mdStringArg;
+    let yamlString: string | undefined;
     const result = await plugins.unified()
       .use(plugins.remarkParse)
       .use(plugins.remarkGfm)
       .use(plugins.remarkFrontmatter, ['yaml', 'toml'])
       .use(plugins.remarkStringify)
       .use(plugins.remarkHtml)
-      .use(() => (tree) => {
-        console.dir(tree);
-        const yamlChild = tree.children.find(objectArg => objectArg.type === 'yaml');
+      .use((): plugins.Transformer<plugins.Root> => (tree) => {
+        const yamlChild = tree.children.find(isYamlNode);
         if (yamlChild) {
-          yamlString = (yamlChild as any).value;
+          yamlString = yamlChild.value;
         }
       })
       .process(mdStringArg);