【编译技术】：解读 Babel AST Format——06

2020-11-05 10:24:57 浏览数 (1)

1. 什么是 Babel AST Format？

The Babel parser generates AST according to Babel AST format. It is based on ESTree spec with some deviations.

2. 本期涉及哪些 AST node types？

本期涉及：

  • Identifier
  • Literals
    • RegExpLiteral
    • NullLiteral
    • StringLiteral
    • BooleanLiteral
    • NumericLiteral
    • BigIntLiteral
  • Programs
  • Function
  • Statements
    • ExpressionStatement
    • BlockStatement
    • EmptyStatement
    • DebuggerStatement
    • WithStatement
    • Control flow
      • ReturnStatement
      • LabeledStatement
      • BreakStatement
      • ContinueStatement
    • Choice
      • IfStatement
      • SwitchStatement
        • SwitchCase
    • Exceptions
      • ThrowStatement
      • TryStatement
        • CatchClause
    • Loops
      • ‍WhileStatement
      • DoWhileStatement
      • ForStatement
      • ForInStatement
      • ForOfStatement
    • Declarations
      • FunctionDeclaration
      • VariableDeclaration
        • VariableDeclarator

3. 示例

3.1. Identifier

AST：An identifier.

代码语言：javascript复制
export interface Identifier extends BaseNode {
  type: "Identifier";
  name: string;
  decorators: Array<Decorator> | null;
  optional: boolean | null;
  typeAnnotation: TypeAnnotation | TSTypeAnnotation | Noop | null;
}

3.2. Program

AST：A complete program source tree.

  • Parsers must specify sourceType as "module" if the source has been parsed as an ES6 module. Otherwise, sourceType must be "script".
代码语言：javascript复制
export interface Program extends BaseNode {
  type: "Program";
  body: Array<Statement>;
  directives: Array<Directive>;
  sourceType: "script" | "module";
  interpreter: InterpreterDirective | null;
  sourceFile: string;
}

3.3. Literals

AST：A literal token. May or may not represent an expression.

代码语言：javascript复制
export type Literal = StringLiteral | NumericLiteral | NullLiteral | BooleanLiteral | RegExpLiteral | TemplateLiteral | BigIntLiteral | DecimalLiteral;

export interface StringLiteral extends BaseNode {
  type: "StringLiteral";
  value: string;
}

export interface NumericLiteral extends BaseNode {
  type: "NumericLiteral";
  value: number;
}

export interface NullLiteral extends BaseNode {
  type: "NullLiteral";
}

export interface BooleanLiteral extends BaseNode {
  type: "BooleanLiteral";
  value: boolean;
}

export interface RegExpLiteral extends BaseNode {
  type: "RegExpLiteral";
  pattern: string;
  flags: string;
}

export interface TemplateLiteral extends BaseNode {
  type: "TemplateLiteral";
  quasis: Array<TemplateElement>;
  expressions: Array<Expression>;
}

export interface BigIntLiteral extends BaseNode {
  type: "BigIntLiteral";
  value: string;
}

export interface DecimalLiteral extends BaseNode {
  type: "DecimalLiteral";
  value: string;
}

示例：

代码语言：javascript复制
"webj2ee", 123, null, true, /^regex$/, 456n, `template`

3.4. Function

AST：A function declaration or expression.

代码语言：javascript复制
export type Function = FunctionDeclaration | FunctionExpression | ObjectMethod | ArrowFunctionExpression | ClassMethod | ClassPrivateMethod;

3.5. Statements——ExpressionStatement

AST：An expression statement, i.e., a statement consisting of a single expression.

代码语言：javascript复制
export type Statement = BlockStatement | BreakStatement | ContinueStatement | DebuggerStatement | DoWhileStatement | EmptyStatement | ExpressionStatement | ForInStatement | ForStatement | FunctionDeclaration | IfStatement | LabeledStatement | ReturnStatement | SwitchStatement | ThrowStatement | TryStatement | VariableDeclaration | WhileStatement | WithStatement | ClassDeclaration | ExportAllDeclaration | ExportDefaultDeclaration | ExportNamedDeclaration | ForOfStatement | ImportDeclaration | DeclareClass | DeclareFunction | DeclareInterface | DeclareModule | DeclareModuleExports | DeclareTypeAlias | DeclareOpaqueType | DeclareVariable | DeclareExportDeclaration | DeclareExportAllDeclaration | InterfaceDeclaration | OpaqueType | TypeAlias | EnumDeclaration | TSDeclareFunction | TSInterfaceDeclaration | TSTypeAliasDeclaration | TSEnumDeclaration | TSModuleDeclaration | TSImportEqualsDeclaration | TSExportAssignment | TSNamespaceExportDeclaration;

export interface ExpressionStatement extends BaseNode {
  type: "ExpressionStatement";
  expression: Expression;
}

示例：

代码语言：javascript复制
x

3.6. Statements——BlockStatement

AST：A block statement, i.e., a sequence of statements surrounded by braces.

代码语言：javascript复制
export interface BlockStatement extends BaseNode {
  type: "BlockStatement";
  body: Array<Statement>;
  directives: Array<Directive>;
}

示例：

代码语言：javascript复制
{}

3.7. Statements——EmptyStatement

AST：An empty statement, i.e., a solitary semicolon.

代码语言：javascript复制
export interface EmptyStatement extends BaseNode {
  type: "EmptyStatement";
}

示例：

代码语言：javascript复制
;;;;

3.8. Statements——DebuggerStatement

AST：A debugger statement.

代码语言：javascript复制
export interface DebuggerStatement extends BaseNode {
  type: "DebuggerStatement";
}

示例：

代码语言：javascript复制
debugger;

3.9. Statements——WithStatement

AST：A with statement.

代码语言：javascript复制
export interface WithStatement extends BaseNode {
  type: "WithStatement";
  object: Expression;
  body: Statement;
}

示例：

代码语言：javascript复制
with (expression) {}

3.10. Statements——Control flow

3.11. Statements——Choice

AST：

代码语言：javascript复制
// Control flow
export interface ReturnStatement extends BaseNode {
  type: "ReturnStatement";
  argument: Expression | null;
}

export interface LabeledStatement extends BaseNode {
  type: "LabeledStatement";
  label: Identifier;
  body: Statement;
}

export interface BreakStatement extends BaseNode {
  type: "BreakStatement";
  label: Identifier | null;
}

export interface ContinueStatement extends BaseNode {
  type: "ContinueStatement";
  label: Identifier | null;
}

// Choice
export interface IfStatement extends BaseNode {
  type: "IfStatement";
  test: Expression;
  consequent: Statement;
  alternate: Statement | null;
}

export interface SwitchStatement extends BaseNode {
  type: "SwitchStatement";
  discriminant: Expression;
  cases: Array<SwitchCase>;
}

export interface SwitchCase extends BaseNode {
  type: "SwitchCase";
  test: Expression | null;
  consequent: Array<Statement>;
}

示例1：

代码语言：javascript复制
switch(condition){
    case v1:
        break;
}

示例2：

代码语言：javascript复制
function fn(){
    for(;;){
        if(v1)
            return;
        if(v2)
            break;
        if(v3)
            continue;
    }
}

3.12. Statements——Exceptions

AST：

代码语言：javascript复制
export interface TryStatement extends BaseNode {
  type: "TryStatement";
  block: BlockStatement;
  handler: CatchClause | null;
  finalizer: BlockStatement | null;
}

export interface ThrowStatement extends BaseNode {
  type: "ThrowStatement";
  argument: Expression;
}

export interface CatchClause extends BaseNode {
  type: "CatchClause";
  param: Identifier | ArrayPattern | ObjectPattern | null;
  body: BlockStatement;
}

示例：

代码语言：javascript复制
try{
}catch(ex){
    throw ex;
}finally{
}

3.13. Statements——Loops

AST：

代码语言：javascript复制
export type Loop = DoWhileStatement | ForInStatement | ForStatement | WhileStatement | ForOfStatement;
export type While = DoWhileStatement | WhileStatement;

export interface ForStatement extends BaseNode {
  type: "ForStatement";
  init: VariableDeclaration | Expression | null;
  test: Expression | null;
  update: Expression | null;
  body: Statement;
}

export interface ForOfStatement extends BaseNode {
  type: "ForOfStatement";
  left: VariableDeclaration | LVal;
  right: Expression;
  body: Statement;
  await: boolean;
}

export interface ForInStatement extends BaseNode {
  type: "ForInStatement";
  left: VariableDeclaration | LVal;
  right: Expression;
  body: Statement;
}

export interface DoWhileStatement extends BaseNode {
  type: "DoWhileStatement";
  test: Expression;
  body: Statement;
}

export interface WhileStatement extends BaseNode {
  type: "WhileStatement";
  test: Expression;
  body: Statement;
}

示例：

代码语言：javascript复制
for(;;){}
for(let k in o){}
for(let k of o){}
while(condition){}
do{}while(condition)

3.14. Statements——Declarations

AST：

代码语言：javascript复制
export interface FunctionDeclaration extends BaseNode {
  type: "FunctionDeclaration";
  id: Identifier | null;
  params: Array<Identifier | Pattern | RestElement | TSParameterProperty>;
  body: BlockStatement;
  generator: boolean;
  async: boolean;
  declare: boolean | null;
  returnType: TypeAnnotation | TSTypeAnnotation | Noop | null;
  typeParameters: TypeParameterDeclaration | TSTypeParameterDeclaration | Noop | null;
}

export interface VariableDeclaration extends BaseNode {
  type: "VariableDeclaration";
  kind: "var" | "let" | "const";
  declarations: Array<VariableDeclarator>;
  declare: boolean | null;
}

export interface VariableDeclarator extends BaseNode {
  type: "VariableDeclarator";
  id: LVal;
  init: Expression | null;
  definite: boolean | null;
}

示例：

代码语言：javascript复制
function fn(){}
var x, y, z;

参考资料1：

Babel AST Format： https://github.com/babel/babel/blob/master/packages/babel-parser/ast/spec.md

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