While defining a function,
if we include a list of variables
in between the () parentheses,
they are called parameters.
Let's define a new
displayValidationError function,
with parameters this time.
In the example above,
invalidFieldName, additionalMessage
are the function parameters.
They are used inside the
console.log so that
the message displayed
can be modified based on
the value of the parameters.
To call a function
that has parameters,
we need to provide the values
in the function call.
These are called arguments.
In the example given above,
we pass two arguments -
"name", and
"Please provide a valid name.".
This means that
the parameter invalidFieldName
gets the value "name",
and the parameter additionalMessage
gets the value
"Please provide a valid name.".
Let's use this new definition
of displayValidationError in the example
from the beginning of this chapter.
It is important to note that
parameters are the list of variables
wrapped in parentheses ()
in a function definition.
In the example above,
(invalidFieldName, additionalMessage)
are parameters of the function displayValidationError.
Arguments are the values passed
in a function call.
In the above example,
displayValidationError("name", "Please provide a valid name.")
is a function call
and
"name", "Please provide a valid name."
are the arguments.
Consider the following function,
which has only one parameter.
For arrow functions
with only one parameter,
we don't need the
parentheses ()
around the parameters,
as shown below.