# Function Signature (JavaScript)

Functions have a signature, this is how the JavaScript runtime knows what code block to…

## How is a **function** defined in JavaScript?

**Functions** have a signature, this is how the JavaScript
runtime knows what code block to execute when 
the function is called.

In JavaScript, a **global function** begins with the word *function*
, followed by the *name* of the function, and *parentheses* with 
an optional list of parameters.

```javascript
// a function with NO input parameters
function sayHello(){
    console.log('Hello');
}
// a function WITH input parameters
function add(first, second) {
    return first + second;
}
```

Level: Apprentice · [More JavaScript terms at this level](https://www.ask-codey.com/glossary/subjects/javascript/apprentice)

Updated: September 27, 2026

Source: https://www.ask-codey.com/glossary/function-signature-javascript