JavaScript Code Formatter
ガイド
JavaScript Code Formatter
Paste minified, messy, or compressed JavaScript and get back a clean, consistently formatted version you can actually read. The formatter is token-aware — it understands string literals, template literals, regular expressions, and comments, so it never accidentally reformats the inside of a regex or rearranges your ${...} interpolations. Everything runs in your browser, so the code you paste never leaves your machine.
使用方法
- Paste your JavaScript into the input box.
- Pick your indentation, quote style, and semicolon policy.
- Choose a brace style (1TBS or Allman) and a trailing-comma policy.
- Set a target print width — long object literals and arrays are split to fit.
- Copy the formatted output or download it as a
.jsファイル。
機能
- 決定論的出力 – the same input always produces the same result.
- 設定可能なインデント – 2 spaces, 4 spaces, or tabs.
- Quote conversion – switch between single, double, or preserve the original style with safe escape handling.
- Semicolon policy – always insert, strip them all, or preserve what is already there.
- Brace styles – 1TBS (same line) or Allman (next line).
- 終端カンマ – none, ES5 (objects and arrays only), or all (including function arguments).
- Print width wrapping – long literals are split across multiple indented lines.
- Modern syntax – arrow functions, async/await, spread/rest, destructuring, classes, template literals, BigInt, and regex literals are all recognised.
- Comment preservation – inline and block comments survive the format pass.
- Runs locally – your code never leaves the browser.
このツールを使用するタイミング
Reach for this formatter when you are reading minified bundles in the wild, inspecting a third-party snippet, copying code out of a chat or email into a real project, or normalising a teammate’s style before reviewing a pull request. Unlike a full linter, it focuses purely on whitespace and punctuation — your logic stays untouched.
よくある質問
-
What is the difference between a JavaScript minifier and a beautifier?
A minifier strips unnecessary whitespace, shortens identifiers, and removes comments to produce the smallest possible code for shipping to browsers. A beautifier or formatter does the opposite: it expands the code with consistent indentation, line breaks, and spacing so a human can read it. The two are usually used at opposite ends of a workflow — beautify during development, minify before deployment.
-
Why is deterministic formatting better than asking an AI to reformat code?
Deterministic formatters apply the same rules to the same input every time, so a function reformatted today and reformatted next month produces an identical diff. AI models, in contrast, may introduce subtle stylistic drift between runs, occasionally rewrite logic, or invent options that do not exist. For code that ends up in version control, predictable output keeps diffs reviewable and avoids accidental behavior changes.
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What is the 1TBS brace style versus Allman?
1TBS — the One True Brace Style — keeps the opening brace on the same line as the statement that introduces it, as in
function foo() {. Allman style places the opening brace on its own line directly beneath. Both are valid; 1TBS is the dominant convention in modern JavaScript and is the style Prettier and most ESLint presets enforce. -
When should I use trailing commas in JavaScript?
Trailing commas in multi-line arrays and object literals are valid in all modern JavaScript runtimes and produce smaller, cleaner diffs when items are added — the line that previously needed both a comma and a new item now only changes once. Trailing commas in function parameter and argument lists are also legal since ES2017 but are sometimes disabled for compatibility with older tooling. Use ES5 mode if you want commas in objects and arrays but not function calls.
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