JS Tutorials
JS Introduction
JS Syntax
JS Comments
JS Variables
JS Operators
JS Data Types
JS Functions
JS Objects
JS Numbers
JS Arrays
JS Array Methods
JS Booleans
JS Events
JS Strings
JS Dates
JS Maths
JS Objects
Object Definition
Object Properties
Object Methods
Object Display
Object Prototypes
Object Iterables
Object Sets
Object Maps
Object References
JS Functions
Function Definition
Function Parameters
Function Invocation
Function Call
Function Apply
Function ClosuresJS Classes
Class Intro
Class Inhertitance
Class Static
JS Async
JS Callbacks
JS Aysnchronous
JS Promises
JS Sync/Await
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JavaScript Function Parameters
A JavaScript function does not perform any
checking on
parameter values (arguments).
Function Parameters and Arguments
Earlier in this tutorial, you learned that functions can have parameters:
// code to be executed
}
Function parameters are the names listed in the function definition.
Function arguments are the real values passed to (and received by) the function.
Parameter Rules
JavaScript function definitions do not specify data types for parameters.
JavaScript functions do not perform type checking on the passed arguments.
JavaScript functions do not check the number of arguments received.
Default Parameters
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:
Example
if (y === undefined) {
y = 2;
}
}
// function code
}
The Arguments Object
JavaScript functions have a built-in object called 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:
Example
function findMax() {
let max = -Infinity;
for (let i = 0; i < arguments.length; i++) {
if (arguments[i] > max) {
max = arguments[i];
}
}
return max;
}
Or create a function to sum all input values:
Example
function sumAll() {
let sum = 0;
for (let i = 0; i < arguments.length; i++) {
sum += arguments[i];
}
return sum;
}