Default Parameters

To define a default parameter in a function, we use the assignment operator (=) to assign a default value to the parameter within the function declaration. The default value is used when no argument is provided or when an undefined argument is passed.

1function functionName(parameter = defaultValue) {
2  // function body
3}

Examples

Let's go through a few examples to understand how default parameters work:

Example 1: Simple Default Parameter

1function greet(name = "Guest") {
2  console.log(`Hello, ${name}!`);
3}
4
5greet(); // Output: Hello, Guest!
6greet("John"); // Output: Hello, John!

In this example, we define a function greet with a default parameter name set to "Guest". When no argument is passed to the function, it uses the default value and greets the guest. If an argument is provided, it uses the provided name.