Code Conversion Between Languages with AI

Translate code between programming languages accurately

When You Need to Convert Code

• Stack migration: Python → Node.js, PHP → Go
• Multiple platforms: Backend in Java, frontend in TypeScript
• Learning a new language: Translate familiar code
• Porting libraries: JavaScript → Python for ML
• Unifying code: Different languages in the same project

Conversion Prompts

Direct conversion

Conversion with adaptation

Framework conversion

Practical Example

Python (original)

JavaScript (converted)

Most Common Conversions

Watch Out for Differences

• Typing: Python dynamic → TypeScript static
• Error handling: Exceptions vs Result types
• Async: async/await works differently in each language
• Mutability: Some languages are immutable by default
• Standard libraries: Not everything has a direct equivalent

Key Differences Between Popular Languages

Understanding the fundamental differences between languages is essential for accurate conversions. Each language has its own philosophy, paradigms, and conventions that go beyond syntax.

Python vs JavaScript

Python uses indentation to define code blocks, while JavaScript uses curly braces. Python is strongly typed (you can't add a string to a number), while JavaScript is weakly typed (it does automatic coercion). Python uses snake_case for variables and functions, JavaScript uses camelCase. In Python, arrays are called lists and dictionaries are called dicts. Async handling is different: Python uses async/await with asyncio, while JavaScript has it integrated into the event loop.

# Python
def greet(name: str) -> str:
    if not name:
        raise ValueError("Name is required")
    return f"Hello, {name}!"

users = [
    {"name": "Ana", "age": 25},
    {"name": "Carlos", "age": 30},
]
adults = [u for u in users if u["age"] >= 18]

// JavaScript
function greet(name) {
    if (!name) {
        throw new Error("Name is required");
    }
    return `Hello, ${name}!`;
}

const users = [
    { name: "Ana", age: 25 },
    { name: "Carlos", age: 30 },
];
const adults = users.filter(u => u.age >= 18);

Java vs C#

Java and C# are very similar languages, both object-oriented and strongly typed. The main differences are in naming conventions (Java uses camelCase for methods, C# uses PascalCase), properties (C# has native properties, Java uses getters/setters), LINQ vs Streams, and the ecosystem (Maven/Gradle vs NuGet). C# has more modern features like pattern matching, records, and integrated async/await for longer.

// Java
public class User {
    private String name;
    private int age;

    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public int getAge() { return age; }
    public void setAge(int age) { this.age = age; }
}

// C#
public class User
{
    public string Name { get; set; }
    public int Age { get; set; }
}

Go vs Python/JavaScript

Go is radically different from Python and JavaScript. It's statically typed, compiled, and has no exceptions (uses multiple return values for errors). It has no classes or inheritance (uses structs and composition). Its concurrency handling with goroutines and channels is unique. Go favors simplicity and explicitness over magic: no default values, no function overloading, and error handling is always explicit.

# Python
def divide(a, b):
    if b == 0:
        raise ValueError("Cannot divide by zero")
    return a / b

try:
    result = divide(10, 0)
except ValueError as e:
    print(f"Error: {e}")

// Go
func divide(a, b float64) (float64, error) {
    if b == 0 {
        return 0, fmt.Errorf("cannot divide by zero")
    }
    return a / b, nil
}

result, err := divide(10, 0)
if err != nil {
    fmt.Printf("Error: %v\n", err)
}

Common Conversion Patterns

When converting code between languages, there are recurring patterns that appear again and again. Knowing them allows you to anticipate necessary changes and write more precise prompts for the AI.

Data structure conversion

Fundamental data structures have equivalents in each language, but with important differences in behavior and performance. JavaScript arrays are dynamic and heterogeneous, Python lists are similar but with more built-in methods, Go slices are fixed-size by default, and Java ArrayLists require specifying type. Dictionaries/objects/hashmaps are ubiquitous but differ in ordering, available methods, and handling of nonexistent keys.

# Python dictionary
user = {"name": "Ana", "age": 25}
user["email"] = "ana@example.com"
name = user.get("name", "Unknown")

// JavaScript object
const user = { name: "Ana", age: 25 };
user.email = "ana@example.com";
const name = user.name ?? "Unknown";

// Go map
user := map[string]string{"name": "Ana"}
user["email"] = "ana@example.com"
name, ok := user["name"]
if !ok { name = "Unknown" }

// Java HashMap
Map<String, String> user = new HashMap<>();
user.put("name", "Ana");
String name = user.getOrDefault("name", "Unknown");

Async pattern conversion

Asynchrony is one of the most complex aspects to convert. JavaScript uses Promises and async/await with a single-threaded event loop. Python uses asyncio with similar async/await but requires an explicit event loop. Go uses goroutines and channels with a real multi-threaded concurrency model. Java uses CompletableFuture or virtual threads (Java 21+). C# has integrated async/await with the Task Parallel Library.

// JavaScript
async function fetchUser(id) {
    const response = await fetch(`/api/users/${id}`);
    return response.json();
}
const users = await Promise.all(ids.map(fetchUser));

# Python
async def fetch_user(id):
    async with aiohttp.ClientSession() as session:
        async with session.get(f"/api/users/{id}") as resp:
            return await resp.json()
users = await asyncio.gather(*[fetch_user(id) for id in ids])

// Go
func fetchUser(id int) (User, error) {
    var user User
    resp, err := http.Get(fmt.Sprintf("/api/users/%d", id))
    if err != nil { return user, err }
    json.NewDecoder(resp.Body).Decode(&user)
    return user, nil
}
// With goroutines:
ch := make(chan User)
for _, id := range ids {
    go func(id int) { u, _ := fetchUser(id); ch <- u }(id)
}

Error handling conversion

The try/catch pattern from Java, JavaScript, and Python has no direct equivalent in Go, which uses multiple return values. Rust uses the Result type with the ? operator for error propagation. C# uses try/catch similar to Java but with exception filters. When converting, it's fundamental to adapt the error pattern to the target language's idiom, not just translate syntax.

Automatic Transpilation Tools

In addition to AI, there are specialized tools that convert code between languages automatically. These tools are especially useful for large migrations where manual conversion would be too costly.

Babel and the JavaScript ecosystem

Babel is the most popular transpiler in the JavaScript ecosystem. It converts modern JavaScript (ES2024+) to versions compatible with older browsers. It can also transform JSX, Flow types, and experimental proposals. Along with tools like SWC (written in Rust, much faster) and esbuild (written in Go, ultra-fast), they form the core of the compilation chain for frameworks like React, Next.js, and Vite.

// Input (JSX)
const element = <h1 className="title">Hello, {name}!</h1>;

// Output (pure JavaScript)
const element = React.createElement(
  "h1",
  { className: "title" },
  "Hello, ", name, "!"
);

// Configuration babel.config.json
{
  "presets": [
    ["@babel/preset-env", { "targets": "> 0.25%" }],
    "@babel/preset-react"
  ]
}

TypeScript as a transpiler

TypeScript is itself a transpiler that converts TypeScript code (JavaScript with types) to pure JavaScript. The tsc compiler removes all type annotations and generates JavaScript compatible with any environment. Migrating from JavaScript to TypeScript is one of the most common conversions in the industry, and AI can greatly help you infer correct types and configure tsconfig.json properly.

Framework migration tools

There are specialized tools for migrating between frameworks: ngUpgrade for migrating from AngularJS to modern Angular, Vue Codemod for migrating from Vue 2 to Vue 3, React Codemod for migrating class components to hooks. These tools use ASTs (Abstract Syntax Trees) to transform code safely, preserving business logic while adapting syntax to the new framework. AI complements these tools by handling edge cases that automatic transformations don't cover.

Cross-language conversion tools

For conversions between completely different languages, tools like JSweet (Java to TypeScript), Google's J2ObjC (Java to Objective-C for iOS), Sharpen (Java to C#), and Pyjion (Python to CIL/.NET) can automate part of the process. However, these tools usually require significant manual adjustments. The combination of an automatic tool for base conversion and AI for refining and adapting the result is currently the most productive approach.

Frequently Asked Questions