What are the best practices for using union types in TypeScript?

What are the best practices for using union types in TypeScript?

When using union types in TypeScript, it's important to ensure clarity and maintainability. Here are some best practices:

1. Use Descriptive Names: Name your union types clearly to convey their purpose.
2. Limit Complexity: Avoid overly complex unions; keep them manageable.
3. Type Guards: Implement type guards to handle different types safely.
4. Documentation: Document your union types to help other developers understand their usage.

Can you give an example of a union type?

Sure! Here's a simple example:

type Shape = 'circle' | 'square' | 'triangle';

function getArea(shape: Shape, size: number): number {
    switch (shape) {
        case 'circle':
            return Math.PI * size * size;
        case 'square':
            return size * size;
        case 'triangle':
            return (Math.sqrt(3) / 4) * size * size;
        default:
            throw new Error('Unknown shape');
    }
}

In this example, Shape is a union type that can be one of three string literals.

What are type guards and how do I use them?

Type guards are functions or expressions that help TypeScript determine the type of a variable at runtime. You can use them to narrow down the type of a union. For example:

function isCircle(shape: Shape): shape is 'circle' {
    return shape === 'circle';
}

if (isCircle(myShape)) {
    // TypeScript knows myShape is 'circle' here
}

This way, you can safely access properties or methods specific to that type.

Are there any performance considerations with union types?

Generally, union types do not have significant performance overhead. However, excessive complexity in unions can lead to longer compile times and more complex type checking. It's best to keep unions simple and well-defined to maintain performance and readability.