website: add mermaid example. (#238)

Author: jaywcjlove

core/README.md

@@ -180,6 +180,75 @@ export default function Demo() {
 <!--rehype:ignore:start-->Ignored content<!--rehype:ignore:end-->
 ```
 
+## Support Custom Mermaid Preview
+
+```jsx mdx:preview?background=#fff
+import React, { useState, useRef, useId, useEffect, Fragment, useCallback } from "react";
+import MarkdownPreview from '@uiw/react-markdown-preview';
+import { getCodeString } from 'rehype-rewrite';
+import mermaid from "mermaid";
+
+const randomid = () => parseInt(String(Math.random() * 1e15), 10).toString(36);
+const Code = ({ inline, children = [], className, ...props }) => {
+  const demoid = useRef(`dome${randomid()}`);
+  const [container, setContainer] = useState(null);
+  const isMermaid = className && /^language-mermaid/.test(className.toLocaleLowerCase());
+  const code = props.node && props.node.children ? getCodeString(props.node.children) : children[0] || '';
+
+  const reRender = async () => {
+    if (container && isMermaid) {
+      try {
+        const str = await mermaid.render(demoid.current, code);
+        container.innerHTML = str.svg;
+      } catch (error) {
+        container.innerHTML = error;
+      }
+    }
+  }
+
+  useEffect(() => {
+    reRender()
+  }, [container, isMermaid, code, demoid]);
+
+  const refElement = useCallback((node) => {
+    if (node !== null) {
+      setContainer(node);
+    }
+  }, []);
+
+  if (isMermaid) {
+    return (
+      <Fragment>
+        <code id={demoid.current} style={{ display: "none" }} />
+        <code ref={refElement} data-name="mermaid" />
+      </Fragment>
+    );
+  }
+  return <code>{children}</code>;
+};
+
+const source = `
+\`\`\`mermaid
+graph TD;
+    A-->B;
+    A-->C;
+    B-->D;
+    C-->D;
+\`\`\`
+`;
+
+export default function Demo() {
+  return (
+    <MarkdownPreview
+      source={source}
+      components={{
+        code: Code
+      }}
+    />
+  );
+}
+```
+
 ### Options Props
 
 ```typescript

website/package.json

@@ -9,6 +9,7 @@
   "dependencies": {
     "@uiw/react-markdown-preview-example": "^1.5.5",
     "@uiw/react-shields": "^1.1.3",
+    "mermaid": "^10.4.0",
     "react": "~18.2.0",
     "react-dom": "~18.2.0",
     "react-router-dom": "^6.8.1"