Reference

全文基于 https://astexplorer.net/ 网站, 选用 acorn 做 parse

全文有哪些 type

• ExpressionStatement 声明
• BinaryExpression 二进制运算
• Program 整个 js 程序
• Literals 字面量
• Identifier 唯一识别标识符
• UpdateExpression 更新表达式
• AssignmentExpression 赋值表达式

关于解释器如何获取代码

通过逐个扫描全文字符串 code, 进行关键字匹配

1+2+3+4

上面代码转成语法树结构就是, 显而易见的是, 上面是从右到左依次解析.

{
  "type": "Program",
  "start": 0,
  "end": 7,
  "body": [
    {
      "type": "ExpressionStatement", 表达式
      "start": 0,
      "end": 7,
      "expression": {
        "type": "BinaryExpression",
        "start": 0,
        "end": 7,
        "left": {
          "type": "BinaryExpression",
          "start": 0,
          "end": 5,
          "left": {
            "type": "BinaryExpression",  // 二项式运算
            "start": 0,
            "end": 3,
            "left": {
              "type": "Literal",
              "start": 0,
              "end": 1,
              "value": 1,
              "raw": "1"
            },
            "operator": "+",
            "right": {
              "type": "Literal",
              "start": 2,
              "end": 3,
              "value": 2,
              "raw": "2"
            }
          },
          "operator": "+",
          "right": {
            "type": "Literal", // 字面量
            "start": 4,
            "end": 5,
            "value": 3,
            "raw": "3"
          }
        },
        "operator": "+",
        "right": {
          "type": "Literal",   // 字面量
          "start": 6,
          "end": 7,
          "value": 4,
          "raw": "4"
        }
      }
    }
  ],
  "sourceType": "module"
}

const fn = a => a;

{
  "type": "Program",
  "start": 0,
  "end": 18,
  "body": [
    {
      "type": "VariableDeclaration",  // const 变量声明表达式
      "start": 0,
      "end": 18,
      "declarations": [
        {
          "type": "VariableDeclarator",
          "start": 6,
          "end": 17,
          "id": {
            "type": "Identifier",
            "start": 6,
            "end": 8,
            "name": "fn"
          },
          "init": {
            "type": "ArrowFunctionExpression",
            "start": 11,
            "end": 17,
            "id": null,
            "expression": true,
            "generator": false,
            "async": false,
            "params": [
              {
                "type": "Identifier",
                "start": 11,
                "end": 12,
                "name": "a"
              }
            ],
            "body": {
              "type": "Identifier",
              "start": 16,
              "end": 17,
              "name": "a"
            }
          }
        }
      ],
      "kind": "const"
    }
  ],
  "sourceType": "module"
}