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TypeScript Compiler API

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The TypeScript Compiler API provides a powerful way to programmatically interact with the TypeScript compiler. This module will guide you through the basics of using the Compiler API, including setting up your environment, understanding the core concepts, and working with practical examples.

Table of Contents

  1. Introduction to the TypeScript Compiler API
  2. Setting Up the Environment
  3. Core Concepts
  4. Practical Examples
  5. Exercises
  6. Summary

Introduction to the TypeScript Compiler API

The TypeScript Compiler API allows developers to:

  • Programmatically compile TypeScript code.
  • Analyze and transform TypeScript code.
  • Create custom tools and plugins for TypeScript.

Setting Up the Environment

To get started with the TypeScript Compiler API, you need to set up your development environment.

Step 1: Install TypeScript

First, ensure you have TypeScript installed. You can install it globally using npm:

npm install -g typescript

Step 2: Create a New Project

Create a new directory for your project and initialize a new Node.js project:

mkdir ts-compiler-api
cd ts-compiler-api
npm init -y

Step 3: Install TypeScript Locally

Install TypeScript as a development dependency in your project:

npm install typescript --save-dev

Step 4: Install TypeScript Compiler API

Install the TypeScript Compiler API package:

npm install @typescript-eslint/typescript-estree --save-dev

Core Concepts

Compiler Options

Compiler options are settings that control how the TypeScript compiler behaves. These options can be specified in a tsconfig.json file or programmatically.

Program

A Program is an object that represents a collection of source files and their compilation settings. It provides methods to interact with the TypeScript compiler.

SourceFile

A SourceFile represents a single TypeScript file. It contains the abstract syntax tree (AST) of the file, which can be analyzed and transformed.

AST (Abstract Syntax Tree)

The AST is a tree representation of the source code. Each node in the tree represents a construct occurring in the source code.

Practical Examples

Example 1: Creating a Simple Program

Let's create a simple TypeScript program using the Compiler API.

import * as ts from 'typescript';

// Create a source file
const sourceCode = `
    const message: string = "Hello, TypeScript!";
    console.log(message);
`;

// Create a SourceFile object
const sourceFile = ts.createSourceFile('example.ts', sourceCode, ts.ScriptTarget.ES2015, true);

// Create a Program
const program = ts.createProgram(['example.ts'], {});

// Get the TypeChecker
const checker = program.getTypeChecker();

// Print the AST
function printNode(node: ts.Node, indent: string = '') {
    console.log(indent + ts.SyntaxKind[node.kind]);
    node.forEachChild(child => printNode(child, indent + '  '));
}

printNode(sourceFile);

Example 2: Transforming Code

Let's transform the TypeScript code to change all variable names to uppercase.

import * as ts from 'typescript';

// Create a source file
const sourceCode = `
    const message: string = "Hello, TypeScript!";
    console.log(message);
`;

// Create a SourceFile object
const sourceFile = ts.createSourceFile('example.ts', sourceCode, ts.ScriptTarget.ES2015, true);

// Transformer function
function transformer<T extends ts.Node>(context: ts.TransformationContext) {
    return (rootNode: T) => {
        function visit(node: ts.Node): ts.Node {
            if (ts.isVariableDeclaration(node)) {
                const name = node.name.getText();
                const newName = ts.createIdentifier(name.toUpperCase());
                return ts.updateVariableDeclaration(node, newName, node.type, node.initializer);
            }
            return ts.visitEachChild(node, visit, context);
        }
        return ts.visitNode(rootNode, visit);
    };
}

// Apply the transformation
const result = ts.transform(sourceFile, [transformer]);
const transformedSourceFile = result.transformed[0];

// Print the transformed code
const printer = ts.createPrinter();
const newCode = printer.printFile(transformedSourceFile as ts.SourceFile);
console.log(newCode);

Exercises

Exercise 1: Analyze Variable Types

Write a program that analyzes a TypeScript file and prints the types of all variables.

Solution:

import * as ts from 'typescript';

// Create a source file
const sourceCode = `
    const message: string = "Hello, TypeScript!";
    const count: number = 42;
`;

// Create a SourceFile object
const sourceFile = ts.createSourceFile('example.ts', sourceCode, ts.ScriptTarget.ES2015, true);

// Create a Program
const program = ts.createProgram(['example.ts'], {});

// Get the TypeChecker
const checker = program.getTypeChecker();

// Analyze variable types
function analyzeVariableTypes(node: ts.Node) {
    if (ts.isVariableDeclaration(node)) {
        const type = checker.getTypeAtLocation(node);
        console.log(`${node.name.getText()}: ${checker.typeToString(type)}`);
    }
    ts.forEachChild(node, analyzeVariableTypes);
}

analyzeVariableTypes(sourceFile);

Exercise 2: Rename Functions

Write a program that renames all functions in a TypeScript file to have a prefix "my".

Solution:

import * as ts from 'typescript';

// Create a source file
const sourceCode = `
    function greet() {
        console.log("Hello, TypeScript!");
    }
`;

// Create a SourceFile object
const sourceFile = ts.createSourceFile('example.ts', sourceCode, ts.ScriptTarget.ES2015, true);

// Transformer function
function transformer<T extends ts.Node>(context: ts.TransformationContext) {
    return (rootNode: T) => {
        function visit(node: ts.Node): ts.Node {
            if (ts.isFunctionDeclaration(node) && node.name) {
                const newName = ts.createIdentifier('my' + node.name.getText());
                return ts.updateFunctionDeclaration(
                    node,
                    node.decorators,
                    node.modifiers,
                    node.asteriskToken,
                    newName,
                    node.typeParameters,
                    node.parameters,
                    node.type,
                    node.body
                );
            }
            return ts.visitEachChild(node, visit, context);
        }
        return ts.visitNode(rootNode, visit);
    };
}

// Apply the transformation
const result = ts.transform(sourceFile, [transformer]);
const transformedSourceFile = result.transformed[0];

// Print the transformed code
const printer = ts.createPrinter();
const newCode = printer.printFile(transformedSourceFile as ts.SourceFile);
console.log(newCode);

Summary

In this module, you learned about the TypeScript Compiler API, including how to set up your environment, core concepts like compiler options, programs, source files, and the AST. You also explored practical examples of creating and transforming TypeScript code programmatically. Finally, you completed exercises to reinforce your understanding of the TypeScript Compiler API.

Next, you will delve into advanced type manipulation techniques in the next topic.

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