Introduction to Acorn

Acorn is a lightweight, fast, and modern JavaScript parser written in JavaScript. It is specifically designed for ECMAScript standards and offers a modular and flexible approach to parse JavaScript code into an abstract syntax tree (AST). This AST can then be analyzed or transformed by applying various operations. In this blog post, we will delve into the various APIs provided by Acorn and demonstrate their usage with practical code snippets.

Basic Usage of Acorn

  const acorn = require('acorn');
  const code = 'const x = 10;';
  const ast = acorn.parse(code, { ecmaVersion: 2020 });
  console.log(ast);

Parsing with Source Type

  const astModule = acorn.parse('import { readFileSync } from "fs";', { sourceType: 'module' });
  console.log(astModule);

Using Acorn Plugins

  const acornWalk = require('acorn-walk');
  const walk = (node) => {
    acornWalk.simple(node, {
      Literal(node) {
        console.log(`Found a literal: ${node.value}`);
      }
    });
  };
  walk(ast);

Loose Parsing with Acorn

  const acornLoose = require('acorn-loose');
  const looseAst = acornLoose.parse_dammit('var a = +;', { ecmaVersion: 2020 });
  console.log(looseAst);

AST Node Visitor with Acorn Walk

   const acornWalk = require('acorn-walk');
   acornWalk.full(ast, (node) => {
     console.log(node.type);
   });

Acorn Custom Tokenizer

  const tokenizer = acorn.tokenizer(code, { ecmaVersion: 2020 });
  let token;
  while ((token = tokenizer.getToken()).type.label !== "eof") {
    console.log(token);
  }

Full Example App Analyzing Variable Declarations

Let’s build a small app that analyzes JavaScript code to find variable declarations and their initial values.

Code

  const acorn = require('acorn');
  const acornWalk = require('acorn-walk');
  
  const code = `
    const x = 10;
    let y = 20;
    var z;
  `;
  
  const ast = acorn.parse(code, { ecmaVersion: 2020 });
  
  const variables = [];
  acornWalk.simple(ast, {
    VariableDeclarator(node) {
      variables.push({
        name: node.id.name,
        value: node.init ? node.init.value : undefined,
      });
    },
  });
  
  console.log(variables);

This small app will output a list of variable names and their initial values found in the parsed JavaScript code.

Stay tuned for more insights and tips on using Acorn efficiently in your projects!

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