# Passing Functions

In JavaScript, you can pass a function as an argument to another function. This is called "passing a function as a parameter".

For example, consider the following code:

```javascript
const greet = (name) => {
  console.log(`Hello, ${name}!`);
};

const sayHello = (callback) => {
  callback('John');
};

sayHello(greet);  // "Hello, John!"

sayHello((name) => {
  console.log(`Hi, ${name}!`);
});  // "Hi, John!"
```

In this example, we have a function called `greet` that takes a single argument (`name`) and logs a greeting to the console. We also have a function called `sayHello` that takes a single argument (`callback`).

When we call the `sayHello` function and pass the `greet` function as an argument, the `sayHello` function calls the `greet` function and passes it the string `'John'` as an argument. This causes the `greet` function to log the string `"Hello, John!"` to the console.

You can also pass anonymous functions (functions without a name) as arguments. For example:

```javascript
sayHello((name) => {
  console.log(`Hi, ${name}!`);
});  // "Hi, John!"
```

In this case, we are passing an anonymous function that logs a different greeting to the console as an argument to the `sayHello` function.

Passing functions as arguments can be useful when you want to write code that is flexible and can be customized by the caller. For example, you might write a utility function that can perform some operation on an array of data, and allow the caller to specify the operation to be performed by passing a function as an argument.