take Markdown rendering into account before testing the maximum preview length

Author: haschek

CHANGELOG.md

@@ -12,12 +12,16 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/) and this p
     -   component for hiding elements in specific media
 -   `<InlineText />`
     -    force children to get displayed as inline content
+-   `<StringPreviewContentBlobToggler />`
+    - `useOnly` property: specify if only parts of the content should be used for the shortened preview, this property replaces `firstNonEmptyLineOnly`
 
 ### Fixed
 
 -   `<Tag />`
     -   create more whitespace inside `small` tag
     -   reduce visual impact of border
+-   `<StringPreviewContentBlobToggler />`
+    -    take Markdown rendering into account before testing the maximum preview length
 
 ### Changed
 
@@ -32,6 +36,11 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/) and this p
     -   `<GridColumn />`
     -   `<PropertyName />` and `<PropertyValue />`
 
+### Deprecated
+
+-   `<StringPreviewContentBlobToggler />`
+    -    `firstNonEmptyLineOnly` will be removed, is replaced by `useOnly="firstNonEmptyLine"`
+
 ## [25.0.0] - 2025-12-01
 
 This is a major release, and it might be not compatible with your current usage of our library. Please read about the necessary changes in the section about how to migrate.

src/cmem/ContentBlobToggler/ContentBlobToggler.tsx

@@ -58,7 +58,7 @@ export function ContentBlobToggler({
                     {previewContent}
                     {enableToggler && (
                         <>
-                            &hellip;{" "}
+                            {" "}&hellip;{" "}
                             <Link
                                 href="#more"
                                 data-test-id={"content-blob-toggler-more-link"}

src/cmem/ContentBlobToggler/StringPreviewContentBlobToggler.tsx

@@ -1,30 +1,52 @@
 import React from "react";
 
-import { ContentBlobToggler, ContentBlobTogglerProps, Markdown } from "./..";
+import {
+    ContentBlobToggler,
+    ContentBlobTogglerProps,
+    Markdown,
+    utils,
+    InlineText,
+} from "./../../../index";
 
 export interface StringPreviewContentBlobTogglerProps
     extends Omit<ContentBlobTogglerProps, "previewContent" | "enableToggler"> {
     /**
-     The preview content will be cut to this length if it is too long.
+     * The preview content will be cut to this length if it is too long.
      */
     previewMaxLength?: number;
     /**
-     The content string. If it is smaller than previewMaxLength this will be displayed in full, else fullviewContent will be displayed.
+     * The content string.
+     * If it is smaller than `previewMaxLength` this will be displayed in full, else `fullviewContent` will be displayed.
      */
     content: string;
-    /** If only the first non-empty line should be shown in the preview. This will in addition also be shortened according to previewMaxLength. */
-    firstNonEmptyLineOnly?: boolean;
-    /** If enabled the preview is rendered as markdown. */
+    /**
+     * Use only parts of `content` in the preview.
+     * `firstMarkdownSection` uses the content until the first double line return.
+     * Currently overwritten by `firstNonEmptyLineOnly`.
+     */
+    useOnly?: "firstNonEmptyLine" | "firstMarkdownSection";
+    /**
+     * If enabled the preview is rendered as Markdown.
+     */
     renderPreviewAsMarkdown?: boolean;
-    /** White-listing of HTML elements that will be rendered when renderPreviewAsMarkdown is enabled. */
+    /**
+     * White-listing of HTML elements that will be rendered when renderPreviewAsMarkdown is enabled.
+     */
     allowedHtmlElementsInPreview?: string[];
-    /** Allows to add non-string elements at the end of the content if the full description is shown, i.e. no toggler is necessary.
+    /**
+     * Allows to add non-string elements at the end of the content if the full description is shown, i.e. no toggler is necessary.
      * This allows to add non-string elements to both the full-view content and the pure string content.
      */
     noTogglerContentSuffix?: JSX.Element;
+    /**
+     * If only the first non-empty line should be shown in the preview.
+     * This will in addition also be shortened according to `previewMaxLength`.
+     * @deprecated (v26) use `useOnly="firstNonEmptyLine"` instead
+     */
+    firstNonEmptyLineOnly?: boolean;
 }
 
-/** Version of the content toggler for text only content. */
+/** Version of the content toggler for text centric content. */
 export function StringPreviewContentBlobToggler({
     className = "",
     previewMaxLength,
@@ -33,21 +55,42 @@ export function StringPreviewContentBlobToggler({
     content,
     fullviewContent,
     startExtended,
-    firstNonEmptyLineOnly,
+    useOnly,
     renderPreviewAsMarkdown = false,
     allowedHtmlElementsInPreview,
     noTogglerContentSuffix,
+    firstNonEmptyLineOnly,
 }: StringPreviewContentBlobTogglerProps) {
-    const previewMaybeFirstLine = firstNonEmptyLineOnly ? firstNonEmptyLine(content) : content;
-    const previewString = previewMaxLength ? previewMaybeFirstLine.substr(0, previewMaxLength) : previewMaybeFirstLine;
-    const enableToggler = previewString !== content;
+    // need to test `firstNonEmptyLineOnly` until property is removed
+    const useOnlyTest: StringPreviewContentBlobTogglerProps["useOnly"] = firstNonEmptyLineOnly ? "firstNonEmptyLine" : useOnly;
+
+    let previewString = content;
+    switch (useOnlyTest) {
+        case "firstNonEmptyLine":
+            previewString = useOnlyPart(content, regexFirstNonEmptyLine);
+            break;
+        case "firstMarkdownSection":
+            previewString = useOnlyPart(content, regexFirstMarkdownSection);
+    }
+
+    let enableToggler = previewString !== content;
+
     let previewContent = renderPreviewAsMarkdown ? (
         <Markdown key="markdown-content" allowedElements={allowedHtmlElementsInPreview}>
             {previewString}
         </Markdown>
     ) : (
         previewString
     );
+
+    if (
+        previewMaxLength &&
+        utils.reduceToText(previewContent, { decodeHtmlEntities: true }).length > previewMaxLength
+    ) {
+        previewContent = utils.reduceToText(previewContent, { decodeHtmlEntities: true }).slice(0, previewMaxLength);
+        enableToggler = true;
+    }
+
     if (!enableToggler && noTogglerContentSuffix) {
         previewContent = (
             <>
@@ -60,7 +103,7 @@ export function StringPreviewContentBlobToggler({
     return (
         <ContentBlobToggler
             className={className}
-            previewContent={previewContent}
+            previewContent={<InlineText>{previewContent}</InlineText>}
             toggleExtendText={toggleExtendText}
             toggleReduceText={toggleReduceText}
             fullviewContent={fullviewContent}
@@ -70,17 +113,27 @@ export function StringPreviewContentBlobToggler({
     );
 }
 
-const newLineRegex = new RegExp("\r|\n"); // eslint-disable-line
+const regexFirstNonEmptyLine = new RegExp("\r|\n"); // eslint-disable-line
+const regexFirstMarkdownSection = new RegExp("\r\n\r\n|\n\n"); // eslint-disable-line
 
 /**
  * Takes the first non-empty line from a preview string.
  */
 function firstNonEmptyLine(preview: string) {
+    return useOnlyPart(preview, regexFirstNonEmptyLine)
+}
+
+/**
+ * Returns only the first part from a preview string.
+ * Or the full string as fallback.
+ */
+function useOnlyPart(preview: string, regexTest: RegExp): string {
     const previewString = preview.trim();
-    const result = newLineRegex.exec(previewString);
-    return result !== null ? previewString.substr(0, result.index) : previewString;
+    const result = regexTest.exec(previewString);
+    return result !== null ? result.input.slice(0, result.index) : previewString;
 }
 
+
 export const stringPreviewContentBlobTogglerUtils = {
     firstNonEmptyLine,
-};
+};