To use a function, you must define it somewhere in the scope from which you wish to call it.
A function definition (also called a function declaration, or function statement) consists of the function keyword, followed by:
The name of the function.
A list of parameters to the function, enclosed in parentheses and separated by commas.
{...}.return specifies the value returned by the function.The function keyword can be used to define a function inside an expression or it could be anonymous it does not have to have a name.
## Calling functions:
Defining a function does not execute it. Defining it names the function and specifies what to do when the function is called.
## Function scope: Variables defined inside a function cannot be accessed from anywhere outside the function, because the variable is defined only in the scope of the function. However, a function can access all variables and functions defined inside the scope in which it is defined.
## Function parameters: In JavaScript, parameters of functions default to undefined. However, in some situations it might be useful to set a different default value.
With default parameters, a manual check in the function body is no longer necessary.
** example** You can put 1 as the default value for b in the function head:
function multiply(a, b = 1) {
` return a * b;`
}
multiply(5); // 5