Function Parameters and Arguments
Earlier in this tutorial, you learned that functions can have parameters:
Function parameters are the names listed in the function definition.
Function arguments are the real values passed to (and received by) the function.
If a function is called with missing arguments (less than declared), the missing values are set to: undefined
Sometimes this is acceptable, but sometimes it is better to assign a default value to the parameter:
If a function is called with too many arguments (more than declared), these arguments can be reached using the arguments object.
The Arguments Object
The argument object contains an array of the arguments used when the function was called (invoked).
This way you can simply use a function to find (for instance) the highest value in a list of numbers:
Or create a function to sum all input values:
Arguments are Passed by Value
The parameters, in a function call, are the function's arguments.
If a function changes an argument's value, it does not change the parameter's original value.
Changes to arguments are not visible (reflected) outside the function.
Objects are Passed by Reference
Because of this, objects will behave like they are passed by reference:
If a function changes an object property, it changes the original value.
Changes to object properties are visible (reflected) outside the function.