babel ast的初级构建

ast叫做抽象语法树，如babel, eslint, typescript和webpack都是借助了抽象语法树，做语法解析（语法分词和语法分析）。

分析和语法分析在线

https://astexplorer.net/

安装

需要操作 AST 代码，这里，我们需要借助两个库，分别是 @babel/core 和 babel-types。

其中 @babel/core 是 babel 的核心库，用来实现核心转换引擎，babel-types 类型判断，用于生成AST零部件

//babel 核心库，用来实现核心转换引擎
const babel = require('@babel/core')
//类型判断，生成AST零部件
const types = require('babel-types')

//源代码
const code = `const sum=(a,b)=>a+b;` 
let result = babel.transform(code,{
    plugins:[
        {
            visitor
        }
    ]
})

　书写plugin　

1. arrowFunction

 1 let visitor = {
 2     ArrowFunctionExpression(path){
 3         let params = path.node.params;
 4         //创建一个blockStatement
 5         let blockStatement = types.blockStatement([
 6             types.returnStatement(types.binaryExpression(
 7                 '+',
 8                 types.identifier('a'),
 9                 types.identifier('b')
10             ))
11         ]);
12         //创建一个函数
13         let func = types.functionExpression(null, params, blockStatement, false, false);
14         //替换
15         path.replaceWith(func);
16     }
17 };

2.classFunction

 1 const babel = require("@babel/core");
 2 const { functionExpression } = require("babel-types");
 3 //类型判断，生成AST零部件
 4 const types = require("babel-types");
 5 
 6 //源代码
 7 const code = `class Person {
 8     constructor(name) {
 9         this.name=name;
10     }
11     sayName() {
12         return this.name;
13     }
14   }`;
15 const expect = `function Person(name) {
16     this.name = name;
17 }
18 Person.prototype.sayName = function () {
19     return this.name;
20 };`;
21 let visitor = {
22   ClassDeclaration(path) {
23       const {id, body} = path.node;
24       const bbody = body.body[0];
25       let funs = [];
26       const constructor = types.functionDeclaration(id, bbody.params, bbody.body, false, false);
27       funs.push(constructor);
28       const pbody = body.body[1];
29      
30       const source = types.memberExpression(id, types.identifier('prototype'), false);
31       const left = types.memberExpression(source,pbody.key,pbody.computed);
32      const right = types.functionExpression(null, pbody.params, pbody.body, false, false  );
33       const proto = types.assignmentExpression('=', left, right); 
34       funs.push(proto);
35     path.replaceWithMultiple(funs);
36   },
37 };
38 let result = babel.transform(code, {
39   plugins: [
40     {
41       visitor,
42     },
43   ],
44 });
45 console.log(result.code);