AST

定义：抽象语法树，源代码语法结构的一种抽象表示

以树状的形式表现编程语言的语法结构，树上的每个节点都表示源代码中的一种结构

n * n;

[
  { type: { ... }, value: "n",  loc: { ... } },
  { type: { ... }, value: "*",  loc: { ... } },
  { type: { ... }, value: "n",  loc: { ... } },
  ...
]

每个type有一组属性来描述该令牌

{
  type: {
    label: 'name',
    keyword: undefined,
    beforeExpr: false,
    startsExpr: true,
    rightAssociative: false,
    isLoop: false,
    isAssign: false,
    prefix: false,
    postfix: false,
    binop: null,
    updateContext: null
  },
  ...
}

举例

function square(n) {
  return n * n;
}

转换为如下的抽象语法树

- FunctionDeclaration:
  - id:
    - Identifier:
      - name: square
  - params [1]
    - Identifier
      - name: n
  - body:
    - BlockStatement
      - body [1]
        - ReturnStatement
          - argument
            - BinaryExpression
              - operator: *
              - left
                - Identifier
                  - name: n
              - right
                - Identifier
                  - name: n

或是如下的JavaScript对象

{
  type: "FunctionDeclaration",  // 类型 一个函数
  id: {
    type: "Identifier",
    name: "square"
  },
  params: [{   // 参数
    type: "Identifier",
    name: "n"
  }],
  body: {
    type: "BlockStatement",
    body: [{
      type: "ReturnStatement",
      argument: {
        type: "BinaryExpression",
        operator: "*",
        left: {
          type: "Identifier",
          name: "n"
        },
        right: {
          type: "Identifier",
          name: "n"
        }
      }
    }]
  }
}

ast的每一层都有相同的结构，比如type或者其他的

cd ..