Introduction to ast-query

ast-query is a powerful library for analyzing and transforming Abstract Syntax Trees (AST) in JavaScript. It provides a high-level API to make working with ASTs more intuitive and less error-prone. Whether you’re building a code analyzer, a migration tool, or just need to manipulate code programmatically, ast-query is an excellent choice.

Features of ast-query

ast-query offers a range of functionalities:

• Traversing AST nodes
• Querying specific AST node types
• Inserting, updating, and deleting nodes
• Code transformation

Basic Usage

Let’s start by installing ast-query:

  npm install ast-query

Now, let’s see some basic code snippets demonstrating various functionalities of ast-query.

Traversing AST Nodes

To traverse AST nodes, use the following pattern:

  
    const astq = require('ast-query');

    const code = `function greet() { console.log("Hello, world!"); }`;
    const ast = astq.parse(code);

    ast.find('FunctionDeclaration').each(function(node) {
      console.log(node);
    });
  

Querying Specific AST Node Types

You can query specific types of nodes like this:

  
    const functions = ast.find('FunctionDeclaration');
    console.log(functions.size()); // Output the number of functions
  

Inserting Nodes

To insert a node into the AST, use the following example:

  
    const newNode = astq.parse('const newVar = 10;').get(0);
    ast.find('BlockStatement').append(newNode);
  

Updating Nodes

This is how you can update an existing node:

  
    ast.find('Literal').replace('greeting', 'Hello, AST!');
  

Deleting Nodes

To delete a node, you can use the following code:

  
    ast.find('VariableDeclaration').remove();
  

App Example

Here is an example of a simple application using the introduced APIs:

  
    const astq = require('ast-query');

    const code = `
    function greet() {
      console.log("Hello, world!");
    }
    `;

    const ast = astq.parse(code);

    // Add a new variable
    const newVar = astq.parse('const newVar = "New Variable";').get(0);
    ast.find('BlockStatement').append(newVar);

    // Update console.log message
    ast.find('Literal').replace('Hello, world!', 'Hello, Universe!');

    // Delete the new variable for demo purposes
    ast.find('VariableDeclaration').remove();

    console.log(ast.toSource());
  

By using ast-query, you can effectively manipulate the structure of your JavaScript code. This library makes it easier to perform complex transformations with relatively simple code.

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