A function is defined using the function statement. The function statement requires:

• a name for the function,
• a list of parameters-or arguments-that will be passed to the function, and
• a command block that defines what the function does.

function functionName (argument1, argument2) {
  command block
}

The naming of functions follows basically the same rules as variables:

• They cannot include spaces,
• must begin with a letter or an underscores (_),
• and should be meaningful and consistent in style.

The list of arguments (parameters) passed to the function appears in parentheses and is separated by commas. The arguments are used to allow functions to import one or more values from outside the function. Even if the functions does not require arguments or parameters, you must supply the parentheses.