JSX Formatter
GeekFormat JSX Formatter tool, based on Prettier v3 Standalone engine for professional beautification of React JSX/TSX component code. Supports 12 formatting configurations (indentation size, semicolons, quote style, trailing commas, bracket spacing, arrow function parentheses, print width, JSX single quotes, JSX bracket same line, property quote strategy, etc.), built-in Terser minification engine, provides JavaScript/TypeScript/JSX/TSX/CSS/HTML/JSON seven language switching. CodeMirror 6 syntax highlighting editor, left-right split panel real-time comparison, supports file upload/download, history records, URL sharing, one-click copy. Pure browser-side processing, no code upload to server.
Related
About JSX Formatting
JSX stands for JavaScript XML, a JavaScript syntax extension introduced by the React framework that allows writing HTML-like tag structures directly in JavaScript code. JSX is converted to regular React.createElement() function calls at compile time by tools like Babel or TypeScript. JSX makes component code structure more intuitive, allowing developers to describe UI structure like writing HTML while gaining the full expressive power of JavaScript. However, if JSX code lacks standardized formatting — messy tag nesting levels, disordered attribute arrangement, inconsistent indentation — it will seriously affect readability and maintenance efficiency, which is also the value of JSX formatting tools.
Prettier is currently the most mainstream code formatting tool in the JavaScript/JSX ecosystem, created by James Long in 2017, and has now become the de facto standard. Prettier's core concept is "opinionated formatter" — it provides only a few configurable items, and the rest of the rules are built-in and unmodifiable. The advantage of this approach is eliminating endless arguments about code style between teams. Prettier supports multiple languages and formats such as JSX/TSX/JavaScript/TypeScript/JSON/CSS/HTML/Markdown, and is widely adopted by mainstream framework communities such as React, Vue, and Angular. Most modern frontend projects integrate Prettier in CI/CD pipelines to ensure consistent code style.
Core rules of JSX formatting include: First, indentation levels — each nested JSX tag and expression increases one level of indentation, reflecting the DOM tree structure; Second, attribute arrangement — when a tag has multiple attributes and exceeds line width, each attribute occupies its own line and is aligned; Third, bracket handling — multi-line JSX expressions are usually wrapped in parentheses to prevent Automatic Semicolon Insertion (ASI) issues; Fourth, self-closing tags — components without child elements use the <Component /> form; Fifth, string quotes — JSX attributes default to double quotes (consistent with HTML), JavaScript strings default to single quotes; Sixth, whitespace handling — whether to add spaces on both sides of curly braces {} inside tags is configurable.
JSX minification is the reverse operation of formatting, with the purpose of converting JSX into the smallest executable code volume, used for production deployment to reduce network transmission volume and speed up loading. JSX minification usually includes the following steps: first compile JSX into React.createElement calls (i.e., regular JavaScript) using Babel, then use a minifier (such as Terser, UglifyJS) to: remove comments and whitespace characters, shorten variable names and function names (mangling), eliminate dead code (dead code elimination), simplify expressions and conditional statements, merge declarations, inline functions, etc. Modern build tools (Webpack, Vite, Rollup) automatically execute code minification in production mode.
Why is code formatting important? In team collaboration, unified code style can greatly improve readability and review efficiency. If every developer formats code according to their own preferences, Git diff will be filled with a large number of meaningless format changes, making it difficult for reviewers to find real logical changes. Research shows that developers spend far more time reading code than writing code, and consistent formatting style can significantly reduce reading cognitive load. Large companies like Google, Meta, and Airbnb all have strict code style specifications and automated formatting toolchains, which is also a reflection of software engineering maturity.
The division of labor between Prettier and Linters (such as ESLint, TSLint) is the best practice of modern frontend engineering: Prettier specializes in formatting — line breaks, indentation, spaces, semicolons, quotes, commas and other pure style issues; ESLint specializes in code quality — unused variables, potential bugs, security issues, best practices and other logical issues. When using both together, you need to turn off overlapping formatting rules in ESLint through eslint-config-prettier to avoid conflicts. Many teams also configure pre-commit hooks (through husky + lint-staged) to automatically run Prettier and ESLint before code submission, ensuring that committed code meets specifications.
Several factors need to be considered when choosing a JSX formatting tool: First, engine selection — prioritize choosing Prettier as the engine, because it is the community standard, results are predictable and consistent with IDE extensions; Second, configurability — choose the number of adjustable parameters according to team needs, too many options instead increase decision cost; Third, security — ensure the tool processes code locally, does not upload to servers, avoids source code leakage risks; Fourth, additional features — minification, syntax highlighting, history records, sharing and other features can improve usage efficiency; Fifth, multi-language support — one tool covering multiple languages such as JS/TS/JSX/TSX/CSS/HTML/JSON can reduce tool switching costs.
Security precautions for using online code formatting tools: First, prioritize choosing tools with pure browser-side processing — such tools do not need servers, code only runs locally, with the highest security; Second, do not paste code containing sensitive information — such as database passwords, API keys, internal business logic, proprietary algorithms, etc., even if the tool claims not to upload, maintain security awareness; Third, check whether the tool uses HTTPS — prevent eavesdropping during transmission (although locally processed tools do not need transmission, the page itself also needs secure loading); Fourth, use local tools for important code — for core business code, it is recommended to use locally installed Prettier CLI or IDE extensions, not relying on online services; Fifth, regularly review tool credibility — check whether it is open source, what the community reviews are like, whether there is a privacy policy, etc.
Use Cases
- React component code copied from the internet with messy formatting, quickly format for easy reading and learning
- Organize JSX component files when taking over legacy projects, unify code style before secondary development
- Format before code review, eliminate meaningless diffs caused by format differences, focus on logic review
- De-format minified JSX production code, read obfuscated code when troubleshooting production issues
- Beautify JSX example code before writing technical blogs or documentation, improve content professionalism
- Compare effects of different formatting configurations, reference for team Prettier configuration selection
- Demonstrate the formatting process of JSX code from messy to standardized in teaching presentations
- When debugging React code snippets online, format first then analyze structure and locate bugs
- In component library documentation that generates JSX code, ensure example code style is unified and beautiful
- Organize your React project code before interviews, ensure submitted code samples follow style standards
- Format AI-generated JSX code before putting into projects, eliminate inconsistent formatting from AI output
- Quickly format component code snippets online when developing React Native or Next.js projects
How to Use
- Paste JSX/TSX code in the left editor, or click the upload button to import .jsx/.tsx files, or load directly from examples
- Click the settings button to adjust formatting parameters: indentation size, semicolons, quotes, trailing commas, print width, JSX options, etc., or keep default configuration
- Click the beautify button (or press shortcut) to execute formatting, the right panel instantly shows formatting results, you can drag left and right to adjust panel width
- If minification is needed, click the minify button to switch to minification mode, the Terser engine will output minimized JSX code
- Click the copy button to copy results to clipboard, or click download to save as file, or send to others via share link
Features
- Prettier v3 engine: Based on the industry's most popular Prettier v3 Standalone as the formatting engine, paired with the Babel parser, consistent with the Prettier extension formatting results in VS Code, ensuring unified team code style
- 12 formatting configurations: Adjustable indentation size (2/4/8 spaces or Tab), semicolons, single/double quotes, trailing commas (none/es5/all), bracket spacing, arrow function parentheses, print width, JSX single quotes, JSX bracket same line, property quote strategy, and 12 other parameters
- JSX syntax highlighting editor: Professional code editor based on CodeMirror 6, supporting JSX/TSX syntax highlighting, line numbers, bracket matching, with real-time comparison between left input and right results
- JSX minification feature: Built-in Terser minification engine, one-click minification of JSX component code to minimum size, supporting advanced minification options such as variable name mangling, dead code elimination, console/debugger cleanup, etc.
- 7 languages easily switchable: Supports JavaScript, TypeScript, JSX, TSX, CSS, HTML, JSON — seven commonly used frontend languages, one tool covers full-stack formatting needs
- File upload and download: Supports direct upload and formatting of .jsx/.tsx/.js/.ts/.css/.html/.json files, which can be downloaded and saved locally after processing
- History record panel: Automatically saves recent formatting records, supports backtracking historical versions, and compares formatting effects under different configurations
- One-click copy results: Formatted or minified code can be copied to clipboard with one click, directly pasted into IDE or projects for use
- URL sharing feature: Encodes code and configuration into URL hash via LZ-String compression, copy the link to share complete code and formatting parameters
- Friendly syntax error prompts: Distinguishes syntax errors from other errors when formatting fails, providing localization prompts to help quickly fix code issues
- Draggable split panels: Left and right panel widths can be flexibly adjusted by dragging, adapting to different screen sizes and reading habits
- Browser-local processing: All formatting, minification, and analysis are done in browser JavaScript, code content is not uploaded to any server, source code security is guaranteed
FAQ
What is the principle of JSX formatting? What is its relationship with Prettier?
This tool uses Prettier v3 Standalone version as the underlying formatting engine, parses JSX syntax through the Babel parser, then re-outputs neatly formatted code according to configured rules. Prettier is currently the most popular code formatting tool in the frontend ecosystem, widely used in React/Vue/Angular and other projects. The formatting result of this tool is basically consistent with the result of formatting JSX files with the Prettier extension in VS Code, suitable for quick online formatting without opening local IDE.
What formatting options are supported? Can I customize indentation and quote style?
Supports 12 formatting configurations: 1) Indentation size: 2 spaces/4 spaces/8 spaces or use Tab; 2) Whether to use semicolons; 3) Single quotes or double quotes; 4) Trailing comma strategy: none/es5/all (function parameters also included); 5) Whether there are spaces inside object braces; 6) Whether to add parentheses for single-parameter arrow functions; 7) Print width (maximum characters per line); 8) Whether JSX attributes use single or double quotes; 9) Whether the closing bracket of multi-line JSX is on the same line as content; 10) Object property quote strategy: as-needed/preserve/consistent; 11) HTML whitespace sensitivity; 12) Use Tab indentation. Easily adjustable in the settings panel.
Does formatting change the logic of JSX code? Is it safe?
Formatting only adjusts whitespace characters (line breaks, indentation, spaces) and syntactic sugar forms like quotes and semicolons, it does not change any code logic. Prettier is a mature tool verified by millions of developers worldwide, and formatted code is semantically completely equivalent to the original code. However, note: if the original code itself has syntax errors (such as mismatched brackets, unclosed tags), formatting will fail and prompt a syntax error, in which case you need to fix the code issue first before formatting.
How is the JSX minification feature implemented? What minification options are supported?
JSX minification uses the Terser engine (one of the industry's most popular JavaScript minifiers) executed locally in the browser. Minification includes: removing comments and extra whitespace, variable name shortening and mangling, dead code elimination (dead_code), unused variable removal (unused), function/variable hoisting optimization, conditional expression simplification, loop optimization, etc. Minification first compiles JSX into regular JavaScript through Babel, then performs minification optimization. Note: Minified code has significantly reduced readability, suitable for production deployment, not suitable for development and debugging.
Is TypeScript (TSX) supported? What is the difference from JSX?
Supported. The tool defaults to JSX language, you can switch to TSX mode through the language switch menu in the top left corner. TSX mode uses the TypeScript parser, which can correctly recognize TypeScript type annotations (interface, type, generics, type assertions, etc.), and will not report errors due to type syntax. JSX mode uses the Babel parser, suitable for pure JavaScript React components. TSX minification will automatically remove type annotations first before performing Terser minification.
Will the input JSX code be uploaded to the server? Is privacy and security ensured?
Completely secure. All features of this tool (formatting, minification, syntax detection, history records) are done locally in your browser through JavaScript, code content is not sent over the network to any external server. Prettier and Terser are both pure JavaScript implementation libraries that can run directly on the browser side. You can use this tool while offline, all features still work normally. History records are saved in the browser's localStorage, only visible on your current device.
Where are history records saved? Will they be lost?
History records are saved in the browser's localStorage (local storage), bound to the specific browser and device. If you clear browser data, switch browsers, or use incognito mode, history records will be lost. History records are used to quickly backtrack recently formatted code snippets, convenient for comparing effects of different configurations. It is recommended to save important code as files yourself, and not rely solely on the history record feature.
Does the URL sharing feature upload code to the server?
No. The URL sharing feature compresses code and configuration using LZ-String and encodes them into the hash part of the URL (content after the # sign). URL hash has an important characteristic: it is not sent to the server with HTTP requests, and is only read and parsed by JavaScript locally in the browser. When the recipient opens the share link, the browser directly parses the hash and decompresses to display the code, the entire process does not require server participation. But please note: the share link contains complete code content, if the code is sensitive, do not share it through public channels.
What should I do if formatting fails with a syntax error prompt?
The most common cause of formatting failure is syntax errors in the code itself: 1) JSX tags not closed — check that all tags are paired, self-closing tags are correct (<img /> not <img>); 2) Mismatched brackets — check whether curly braces {}, parentheses (), square brackets [] are paired; 3) Unclosed quotes — whether string quotes are complete; 4) Incorrect syntax — for example, using syntax not allowed in JSX. You can first check the line number and error message in the error prompt to locate the problem, or simplify the code and troubleshoot step by step.
What does print width mean? What value should I set?
Print width (printWidth) is one of Prettier's core parameters, representing the maximum number of characters per line of code. When a line of code exceeds this width, Prettier will automatically wrap it. The default value is 80 characters, which is a long-standing programming convention (originating from punch cards and terminal widths). Common setting values: 80 (classic conservative), 100 (more common), 120 (widescreen friendly). Setting it too small will cause frequent line wrapping making code harder to read, setting it too large makes one line too long to read on narrow screens. It is recommended to choose a value between 80-120 according to team specifications and monitor width.
What is the use of trailing comma? Which mode should I choose?
Trailing comma refers to adding a comma after the last item in multi-line structures such as arrays, objects, function parameters, etc. Benefits include: 1) Adding/removing items only changes one line, Git diff is cleaner; 2) Avoiding syntax errors caused by forgetting to add commas; 3) More stable parsing in some cases. Prettier provides three modes: none (no trailing commas, most concise), es5 (only add where ES5 supports, i.e., arrays and objects, most compatible), all (add wherever possible, including function parameters, requires ES2017+ or Babel/TS support). Modern projects recommend using 'all' mode, which is completely fine with Babel or TypeScript compilation.
What are the effects of JSX single quotes and JSX bracket same line?
JSX single quotes (jsxSingleQuote): Controls whether JSX attribute values use single quotes or double quotes. Default is off (double quotes), which is consistent with HTML attribute conventions. When enabled, attribute strings in JSX will use single quotes. JSX bracket same line (jsxBracketSameLine): Controls whether the closing right angle bracket (/> or >) of multi-line JSX elements is placed at the end of the last line (same line), or on a new line (different line). Default is off (new line), when enabled the right bracket is on the same line as the last attribute. Different teams have different preferences, just choose the style consistent with the project.
Is batch formatting of multiple files supported?
Currently the web version tool is mainly designed for single-file quick formatting scenarios, supporting single file upload processing. If you have a large number of JSX/TSX files that need batch formatting, it is recommended to install the Prettier CLI tool in your project and process them in batches via the command line (e.g., npx prettier --write "src/**/*.jsx"). The underlying engine of this tool is completely consistent with Prettier, with the same formatting results. Future versions may consider adding batch processing features.
Can it be used with ESLint?
Yes. In actual projects, it is recommended to use Prettier for code formatting (line breaks, indentation, spaces, quotes, etc.), and ESLint for code quality (unused variables, potential bugs, best practices, etc.). The best practice for using both together is: 1) Install eslint-config-prettier to turn off formatting rules in ESLint that conflict with Prettier; 2) Run Prettier formatting first, then run ESLint checks. This tool focuses on formatting (what Prettier is good at), and does not include ESLint code checking functionality.
Can it be used on mobile phones? How is the mobile experience?
It can be used in mobile browsers. The tool adopts responsive design, automatically adjusting layout on small screen devices — left-right split panels become top-bottom split panels, and toolbar buttons are optimized for touch-friendly sizes. However, code editing experience on mobile is not as good as on desktop, it is recommended to mainly use it on computers. If you frequently need to process code on mobile devices, it is recommended to use a mobile code editor app that supports Prettier.
Troubleshooting
What should I do if formatting fails with a syntax error prompt?
First confirm whether the code is complete: JSX components usually need export or at least include a function returning JSX. Common syntax errors include: 1) JSX tags not closed — check each opening tag has a corresponding closing tag or self-closing marker; 2) Mismatched curly braces — whether brackets of {} expressions in JSX are paired; 3) Unclosed string quotes — check all single quotes/double quotes/backticks; 4) Using reserved words in JSX — e.g., class should be written as className, for should be written as htmlFor; 5) Multiple root elements — JSX only allows one root element, multiple elements need to be wrapped with <>...</> or <div>. Error messages usually indicate line number and reason, you can locate accordingly.
No response after uploading a file or format is wrong?
First confirm whether the file extension is correct — .jsx/.tsx/.js/.ts/.css/.html/.json files can all be uploaded. If the file extension is not standard, the tool may not correctly recognize the language format, resulting in formatting results not meeting expectations. Solutions: 1) Ensure the file extension is in standard format; 2) After uploading, check whether the language selection in the top left corner is correct, if not you can manually switch; 3) Confirm the file content is plain text not binary; 4) Files that are too large (over 1MB) may cause browser lag, it is recommended to use desktop tools for processing.
Formatted code is different from my local Prettier results?
Possible reasons: 1) Version difference — this tool uses Prettier v3, if your project uses v2 version, some details may differ (such as changes in trailing comma default values); 2) Different configurations — check whether parameters like print width, indentation, quotes, trailing commas are consistent with project configuration; 3) Different parser — JSX uses Babel parser, TSX uses TypeScript parser, confirm correct selection; 4) Plugin difference — if local Prettier has additional plugins installed (such as prettier-plugin-tailwindcss), this tool does not include these plugins. It is recommended to adjust the configuration of this tool to be consistent with the project's .prettierrc.
Code doesn't run properly after JSX minification?
JSX minification uses the Terser engine, which first compiles JSX into regular JavaScript before minification. If code doesn't run after minification, check: 1) Whether minification configuration is too aggressive — e.g., enabling toplevel may change module behavior; 2) Whether eval or dynamic property access is used in code — variable mangling may cause name mismatch; 3) Whether specific function names or class names are depended on — if so, need to enable keep_fnames or keep_classnames options. Production environment minification is recommended to be done using project build tools (Vite/Webpack), which have more complete configuration and plugin ecosystem.
Glossary
- JSX
- Abbreviation for JavaScript XML, a JavaScript syntax extension introduced by React, allowing writing HTML-like tag structures in JS, converted to React.createElement() calls after compilation.
- Prettier
- Currently the most popular opinionated code formatting tool, supporting JS/TS/JSX/TSX/JSON/CSS/HTML/Markdown, etc., has become the de facto standard for frontend code formatting.
- Babel
- JavaScript compiler that can convert new syntax like ES6+/JSX/TS into ES5 code compatible with older browsers, also serves as the underlying engine for Prettier to parse JSX.
- Terser
- The industry's most popular JavaScript/JSX minifier, supporting variable mangling, dead code elimination, code compression, etc., is the default minifier for build tools like Webpack/Vite.
- Print Width
- One of Prettier's core parameters, representing the maximum number of characters per line of code, automatically wraps when exceeding this width. Default 80 characters, common settings are 80/100/120.
- Trailing Comma
- Adding a comma after the last item in multi-line structures such as arrays, objects, function parameters, etc. Can make Git diff cleaner and avoid syntax errors. Prettier supports none/es5/all three modes.
- Mangle
- Variable name/function name shortening technology in code minification, replacing meaningful long variable names with short names like a/b/c, reducing code volume, also increasing reading difficulty.
- Dead Code Elimination
- Minifier optimization technology that removes code that will never be executed (such as code under false conditions, unused variables and functions), reducing production build size.
- CodeMirror
- The browser-side code editor component used by this tool (version 6), providing professional editing features such as syntax highlighting, line numbers, bracket matching, widely used in various online IDEs.
- LZ-String
- LZ compression algorithm implemented in JavaScript, used for efficiently compressing and storing code content in URL hash. High compression ratio and fast decoding speed, suitable for share link scenarios.
- localStorage
- Local key-value storage API provided by browsers, capacity about 5-10MB, data persists (unless actively cleared). This tool uses it to store formatting history records.
- ESLint
- JavaScript/TypeScript static code checking tool (Linter), mainly responsible for code quality and best practices, usually used with Prettier (Prettier manages format, ESLint manages quality).
Supported Languages and File Formats
The tool supports 7 commonly used frontend languages, easily switchable via the top left menu:
| Language | File Extension | Formatting Engine | Minification Engine |
|---|---|---|---|
| JavaScript | .js, .mjs, .cjs | Prettier (Babel) | Terser |
| TypeScript | .ts, .mts, .cts | Prettier (TypeScript) | Terser (types removed first) |
| JSX | .jsx | Prettier (Babel) | Terser |
| TSX | .tsx | Prettier (TypeScript) | Terser (types removed first) |
| CSS | .css | Prettier (PostCSS) | CSSO |
| HTML | .html, .htm | Prettier (HTML) | Custom implementation |
| JSON | .json | Prettier (JSON) | JSON.stringify |
Formatting Configuration Items Overview
12 configurable formatting parameters and their effects:
| Configuration Item | Possible Values | Default Value | Description |
|---|---|---|---|
| tabWidth Indentation Size | 2 / 4 / 8 / Tab | 2 spaces | Number of spaces per indentation level, or use Tab character |
| semi Semicolons | true / false | true | Whether to add semicolons at end of statements |
| singleQuote Single Quotes | true / false | false (double quotes) | Whether JS strings use single or double quotes |
| trailingComma Trailing Comma | none / es5 / all | es5 | Whether to add trailing comma after last item in multi-line structures |
| bracketSpacing Bracket Spacing | true / false | true | Whether to add spaces inside object braces |
| arrowParens Arrow Parentheses | always / avoid | always | Whether to add parentheses for single-parameter arrow functions |
| printWidth Print Width | number (recommended 80-120) | 80 | Maximum characters per line, auto-wrap when exceeded |
| jsxSingleQuote JSX Single Quotes | true / false | false | JSX attribute values use single quotes (default double quotes) |
| jsxBracketSameLine JSX Bracket Same Line | true / false | false | Whether multi-line JSX right bracket is on same line as last attribute |
| quoteProps Property Quotes | as-needed / preserve / consistent | as-needed | When to add quotes to object property names |
JSX Minification Before and After Comparison
Using a typical React component as an example, showing the volume change before and after minification:
| Comparison Item | Formatted (Development) | Minified (Production) | Compression Ratio |
|---|---|---|---|
| Code Size | ~ 2.5 KB | ~ 0.8 KB | ~68% |
| Line Count | ~ 80 lines | 1 line | ~99% |
| Variable Names | Meaningful names | a/b/c/d single letters | — |
| Comments | All comments preserved | All removed | — |
| Readability | High (debuggable and readable) | Very low (machine-readable only) | — |
| Use Cases | Development, debugging, review | Production deployment, CDN distribution | — |
Privacy & Security
All operations of this JSX formatter tool are done completely locally in the browser: the code you input or upload is only formatted and minified in browser JavaScript, and will not be sent over the network to any external server. Prettier and Terser are both pure JavaScript libraries that can run directly on the browser side. History records are saved in browser localStorage (local storage), only visible on the current device and browser. The URL sharing feature compresses code via LZ-String and encodes it in the URL hash part (content after # is not sent to the server). The page does not use Cookie tracking, and does not collect code content input by users. You can use this tool while offline, core features are normally available.
Authoritative References
- prettier.ioPrettier Official Documentation
- terser.orgTerser - JavaScript Minifier
- react.devReact Official Docs - JSX Introduction
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