2nd/10_Wiki/Topics/Frontend/Parser.md

---
id: wiki-2026-0508-parser
title: Parser
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [JS Parser, JavaScript Parser, AST Parser]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [frontend, parser, ast, swc, oxc, babel]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: JavaScript/Rust
  framework: SWC/oxc/Babel
---

# Parser

## 매 한 줄
> **"매 source code → AST 의 변환기"**. 매 tokenizer (lexer) → parser → AST tree. 2026 frontend 매 Babel (JS) → SWC (Rust) → oxc (faster Rust) 의 evolution. Vite 7 / Next 16 / Turbopack 의 내부 매 oxc/SWC.

## 매 핵심

### 매 Pipeline
- **Lexer (Tokenizer)**: 매 character stream → token stream (`const`, `x`, `=`, `1`).
- **Parser**: 매 tokens → AST (Abstract Syntax Tree) — `VariableDeclaration { kind: 'const', declarations: [...] }`.
- **Transformer**: 매 AST 의 modify (JSX → JS, TS → JS, ES2025 → ES5).
- **Generator**: 매 AST → source code (codegen).

### 매 Modern Parsers (2026)
- **oxc** (Boshen, Rust): 매 fastest — Babel 의 50-100×, SWC 의 3×. Vite 7 default.
- **SWC** (Vercel, Rust): 매 Next.js / Turbopack 의 backbone. Babel 의 20×.
- **Babel** (JS): 매 legacy ecosystem 의 최대 plugin 호환성. 매 새 project 에서 비추.
- **esbuild** (Go): 매 bundler 내장 parser — Vite dev 의 default.
- **Acorn**: 매 ESLint 9 의 default parser.

### 매 응용
1. Bundling: 매 Vite/Webpack/Turbopack 의 module graph 빌드.
2. Linting: 매 ESLint/Biome 의 rule 적용.
3. Type checking: 매 TS Compiler / SWC `@swc/plugin-tsc`.
4. Code transformation: 매 JSX, TS, decorator, JSX-runtime, optional chaining.

## 💻 패턴

### Babel 의 AST 분석
```js
import * as parser from '@babel/parser';
import traverse from '@babel/traverse';

const code = `const x = 1 + 2;`;
const ast = parser.parse(code, { sourceType: 'module' });

traverse(ast, {
  BinaryExpression(path) {
    if (path.node.operator === '+') {
      console.log('Found addition:', path.node.left.value, '+', path.node.right.value);
    }
  },
});
```

### SWC programmatic
```js
import { parse, transform } from '@swc/core';

const ast = await parse('const x: number = 1;', {
  syntax: 'typescript',
  target: 'es2022',
});

const { code } = await transform('const x: number = 1;', {
  jsc: { parser: { syntax: 'typescript' }, target: 'es2020' },
});
```

### oxc parser (Rust crate)
```rust
use oxc_allocator::Allocator;
use oxc_parser::Parser;
use oxc_span::SourceType;

let allocator = Allocator::default();
let source = "const x = 1;";
let source_type = SourceType::default();
let ret = Parser::new(&allocator, source, source_type).parse();
println!("{:#?}", ret.program);
```

### Custom Babel plugin
```js
export default function ({ types: t }) {
  return {
    visitor: {
      Identifier(path) {
        if (path.node.name === 'foo') {
          path.node.name = 'bar';
        }
      },
    },
  };
}
```

### AST node 직접 생성
```js
import * as t from '@babel/types';
const node = t.variableDeclaration('const', [
  t.variableDeclarator(t.identifier('x'), t.numericLiteral(42)),
]);
// → const x = 42;
```

### ESLint custom rule
```js
export default {
  create(context) {
    return {
      VariableDeclaration(node) {
        if (node.kind === 'var') {
          context.report({ node, message: 'Use let/const instead of var' });
        }
      },
    };
  },
};
```

## 매 결정 기준
| 상황 | Parser |
|---|---|
| New Vite project | oxc (default) |
| Next.js / Turbopack | SWC (built-in) |
| Custom transform plugin (rich ecosystem) | Babel |
| Bundler dev mode | esbuild |
| Lint custom rule | Acorn (ESLint default) |
| Rust toolchain | oxc |

**기본값**: oxc 또는 SWC — 2026 매 Babel 의 production 사용 비추.

## 🔗 Graph
- 부모: [[AST]]
- 변형: [[SWC]] · [[esbuild]]
- 응용: [[Vite]] · [[Turbopack]] · [[ESLint]] · [[Biome]]
- Adjacent: [[Source_Maps]]

## 🤖 LLM 활용
**언제**: codemod 작성, 매 lint rule, custom transformer (CSS-in-JS extraction, dead code elimination).
**언제 X**: 매 simple regex 로 충분한 substitution — AST overkill.

## ❌ 안티패턴
- **Regex 로 JS parsing**: 매 nested template literal / comment 를 매번 break.
- **Babel new project**: 매 SWC/oxc 의 50× 빠름 — legacy plugin 없으면 마이그레이션.
- **AST mutation in place**: 매 path API 사용 — direct node assignment 시 traversal 깨짐.

## 🧪 검증 / 중복
- Verified (oxc 0.40, SWC 1.10, Babel 8 docs, Vite 7 release notes).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — modern parser landscape (oxc/SWC) 강조 |