How do I set default values for function parameters in TypeScript?

How do I set default values for function parameters in TypeScript?

In TypeScript, you can set default values for function parameters by assigning a value in the function signature. For example:

function greet(name: string = 'Guest') {
    return `Hello, ${name}!`;
}

This way, if no argument is provided, 'Guest' will be used as the default.

Can I use default values with optional parameters?

Yes, you can use default values with optional parameters. Just define the parameter with a question mark and assign a default value:

function greet(name?: string) {
    const userName = name || 'Guest';
    return `Hello, ${userName}!`;
}

In this case, if no name is provided, 'Guest' will be used.

What happens if I provide an undefined value?

If you provide undefined as an argument, the default value will be used. For example:

greet(undefined);

This will return 'Hello, Guest!'. However, if you provide null, it will not use the default value.

Can I set default values for rest parameters?

No, you cannot set default values for rest parameters directly. However, you can handle it inside the function. For example:

function logMessages(...messages: string[]) {
    if (messages.length === 0) {
        messages = ['No messages provided.'];
    }
    console.log(messages);
}

This way, you can provide a default message if no messages are passed.