テキストから HTML タグを取り除く方法

问题

HTML コンテンツがあり、タグやマークアップのないプレーンテキストが必要です。

前提条件

• HTML 構造の理解
• HTML エンティティに関する知識

ステップ

1. 1. Parse the HTML

   Use an HTML parser rather than a regex to strip tags. A parser correctly handles nested tags, attributes with > characters, and self-closing tags. Regex-based stripping can fail on edge cases like <script> blocks or attribute values containing >.

   入力

   <p>Hello <b>world</b></p>

   输出

   parsed structure

2. 2. Extract text content

   Walk the parsed DOM and collect text nodes. Skip script and style elements whose content is not visible text. Handle <br> as line breaks and <p> as paragraph breaks. The result is the visible text content.

   入力

   <p>Hello <b>world</b></p>

   输出

   Hello world

3. 3. Decode HTML entities

   After stripping tags, decode HTML entities (&amp; → &, &lt; → <, &#39; → ', &nbsp; → space). This recovers the original characters that were escaped in the HTML. Use a standard entity decoder for the full named and numeric entity set.

   入力

   & < '

   输出

   & < '

期待される結果

HTML タグがすべて除去され、エンティティがデコードされたプレーンテキスト。

よくあるエラー

Using regex to strip tags fails on edge cases

Use a proper HTML parser. Regex cannot correctly handle nested tags, attributes with >, or CDATA sections.

Script content appears in output

Explicitly skip <script> and <style> elements when extracting text. Their content is code, not visible text.

トラブルシューティング指引

• If entities appear as literal text, run an entity decoder after stripping.
• If whitespace is wrong, normalize spaces and line breaks after extraction.

セキュリティ上の制限

• Stripping HTML tags prevents XSS in display contexts, but always also sanitize any remaining text for safe output.