Espree

Espree 是 ESLint 使用的 JavaScript 解析器，基于 Acorn 实现，结合 Acorn-JSX 插件也可解析 React.js JSX。
Espree 将 JavaScript 解析成 AST ，再将 AST Node 传递给 ESLint rule 获得 report 给开发工具，在代码中错误和不符合规范的地方给予开发者提示。当我们在开发 ESLint 规则时，node 将作为参数获取，用于分析代码风格。
以下是解析一段 js 代码的示例：

// demo.js
const a = "123";
console.log("xxx", a);
const jsx = <div className="test">{a}</div>
const issueName = { a: 123, b: 123, c: 123 };
for (let i = 0; i < 99; i++) {
  console.log('xxx', i)
}
if (1 > 0) {
  console.log('xxx', true)
}

// 使用 espree 解析 demo.js 文件
import { readFile, writeFile } from "fs/promises";
import * as espree from "espree";
// 解析成 AST 并保存
async function parseSave(code) {
  const node = espree.parse(code, {
    ecmaVersion: 11,
    ecmaFeatures: { jsx: true },
  })
  await writeFile("./file/nodeResult.json", JSON.stringify(node, null, 4))
}
// 解析成 token 并保存
async function tokenSave(code) {
  const token = espree.tokenize(code, {
    ecmaVersion: 11,
    ecmaFeatures: { jsx: true },
  })
  await writeFile("./file/tokenResult.json", JSON.stringify(token, null, 4))
}
async function parseFile(filePath) {
  const file = readFile(filePath, { encoding: "utf-8" })
  const code = await file
  parseSave(code)
  tokenSave(code)
}
parseFile('./file/demo.js')

// tokenResult.json 解析为 token 结果（部分）
[
    {
        "type": "Keyword",
        "value": "const",
        "start": 0,
        "end": 5
    },
      // ...
  ]

// nodeResult.json 解析为 node 结果（部分）
{
    "type": "Program",
    "start": 0,
    "end": 233,
    "body": [
        {
            "type": "VariableDeclaration",
            "start": 0,
            "end": 16,
            "declarations": [
                {
                    "type": "VariableDeclarator",
                    "start": 6,
                    "end": 15,
                    "id": {
                        "type": "Identifier",
                        "start": 6,
                        "end": 7,
                        "name": "a"
                    },
                    "init": {
                        "type": "Literal",
                        "start": 10,
                        "end": 15,
                        "value": "123",
                        "raw": "\"123\""
                    }
                }
            ],
            "kind": "const"
        },
          // ...
    ],
    "sourceType": "script"
}

// VisitorKeys.json AST 中的 node 类型，
// 通过 espree.VisitorKeys 获取，
// 用于遍历 AST（all visitor keys for traversing the AST）
{
    "AssignmentExpression": ["left", "right"],
    "AssignmentPattern": ["left", "right"],
    "ArrayExpression": ["elements"],
    "ArrayPattern": ["elements"],
    "ArrowFunctionExpression": ["params", "body"],
    "AwaitExpression": ["argument"],
    "BlockStatement": ["body"],
    "BinaryExpression": ["left", "right"],
    "BreakStatement": ["label"],
    "CallExpression": ["callee", "arguments"],
    "CatchClause": ["param", "body"],
    "ChainExpression": ["expression"],
    "ClassBody": ["body"],
    "ClassDeclaration": ["id", "superClass", "body"],
    "ClassExpression": ["id", "superClass", "body"],
    "ConditionalExpression": ["test", "consequent", "alternate"],
    "ContinueStatement": ["label"],
    "DebuggerStatement": [],
    "DoWhileStatement": ["body", "test"],
    "EmptyStatement": [],
    "ExportAllDeclaration": ["exported", "source"],
    "ExportDefaultDeclaration": ["declaration"],
    "ExportNamedDeclaration": ["declaration", "specifiers", "source"],
    "ExportSpecifier": ["exported", "local"],
    "ExpressionStatement": ["expression"],
    "ExperimentalRestProperty": ["argument"],
    "ExperimentalSpreadProperty": ["argument"],
    "ForStatement": ["init", "test", "update", "body"],
    "ForInStatement": ["left", "right", "body"],
    "ForOfStatement": ["left", "right", "body"],
    "FunctionDeclaration": ["id", "params", "body"],
    "FunctionExpression": ["id", "params", "body"],
    "Identifier": [],
    "IfStatement": ["test", "consequent", "alternate"],
    "ImportDeclaration": ["specifiers", "source"],
    "ImportDefaultSpecifier": ["local"],
    "ImportExpression": ["source"],
    "ImportNamespaceSpecifier": ["local"],
    "ImportSpecifier": ["imported", "local"],
    "JSXAttribute": ["name", "value"],
    "JSXClosingElement": ["name"],
    "JSXElement": ["openingElement", "children", "closingElement"],
    "JSXEmptyExpression": [],
    "JSXExpressionContainer": ["expression"],
    "JSXIdentifier": [],
    "JSXMemberExpression": ["object", "property"],
    "JSXNamespacedName": ["namespace", "name"],
    "JSXOpeningElement": ["name", "attributes"],
    "JSXSpreadAttribute": ["argument"],
    "JSXText": [],
    "JSXFragment": ["openingFragment", "children", "closingFragment"],
    "Literal": [],
    "LabeledStatement": ["label", "body"],
    "LogicalExpression": ["left", "right"],
    "MemberExpression": ["object", "property"],
    "MetaProperty": ["meta", "property"],
    "MethodDefinition": ["key", "value"],
    "NewExpression": ["callee", "arguments"],
    "ObjectExpression": ["properties"],
    "ObjectPattern": ["properties"],
    "PrivateIdentifier": [],
    "Program": ["body"],
    "Property": ["key", "value"],
    "PropertyDefinition": ["key", "value"],
    "RestElement": ["argument"],
    "ReturnStatement": ["argument"],
    "SequenceExpression": ["expressions"],
    "SpreadElement": ["argument"],
    "StaticBlock": ["body"],
    "Super": [],
    "SwitchStatement": ["discriminant", "cases"],
    "SwitchCase": ["test", "consequent"],
    "TaggedTemplateExpression": ["tag", "quasi"],
    "TemplateElement": [],
    "TemplateLiteral": ["quasis", "expressions"],
    "ThisExpression": [],
    "ThrowStatement": ["argument"],
    "TryStatement": ["block", "handler", "finalizer"],
    "UnaryExpression": ["argument"],
    "UpdateExpression": ["argument"],
    "VariableDeclaration": ["declarations"],
    "VariableDeclarator": ["id", "init"],
    "WhileStatement": ["test", "body"],
    "WithStatement": ["object", "body"],
    "YieldExpression": ["argument"]
}