Introduction to AST Query

Welcome to our comprehensive guide on AST Query. This powerful tool is designed to provide extensive manipulation and traversal capabilities for your Abstract Syntax Trees (ASTs). In this guide, we’ll cover dozens of useful APIs with practical code snippets.

API Examples

Parsing Code into AST

To start working with AST, first, you’ll need to parse your source code into an AST:

  const { parse } = require('ast-query');
  const ast = parse('const x = 42;');
  console.log(ast);

Finding Nodes

Using the find method, you can locate specific nodes within your AST:

  const nodes = ast.find('VariableDeclarator');
  console.log(nodes.length); // Outputs: 1

Manipulating Nodes

Next, let’s manipulate the nodes:

  nodes.replace('init', { type: 'Literal', value: 99 });
  console.log(ast.toSource());

Removing Nodes

You can also remove nodes:

  const nodesToRemove = ast.find('VariableDeclaration');
  nodesToRemove.remove();
  console.log(ast.toSource());

Inserting Nodes

Add new nodes to your AST:

  ast.get('body').unshift({ type: 'VariableDeclaration', declarations: [{ id: { type: 'Identifier', name: 'y' }, init: { type: 'Literal', value: 0 }, kind: 'const' }]});
  console.log(ast.toSource());

Creating a Simple Application with AST Query

Let’s create a simple application that optimizes JavaScript code by renaming variables for minification:

  const { parse } = require('ast-query');
  const code = `
    function add(a, b) {
      return a + b;
    }
    const x = add(1, 2);
  `;
  const ast = parse(code);
  const vars = ast.find('Identifier');
  vars.each((node, i) => {
    node.replace({ type: 'Identifier', name: `_${i}` });
  });
  console.log(ast.toSource());

By using this method, you can optimize your code by reducing variable name sizes, which significantly contributes to smaller file sizes and better performance.

Conclusion

In this guide, we dived into the functionalities of AST Query, exploring its fundamental APIs and demonstrating their practical usages. We hope this guide has been useful and has provided you with insights to manipulate and optimize your code effectively.