Low Navy Heathrow Shoe DC Top SE zZxEwnq8 Low Navy Heathrow Shoe DC Top SE zZxEwnq8 Low Navy Heathrow Shoe DC Top SE zZxEwnq8 Low Navy Heathrow Shoe DC Top SE zZxEwnq8 Low Navy Heathrow Shoe DC Top SE zZxEwnq8 Low Navy Heathrow Shoe DC Top SE zZxEwnq8

JS Tutorial

JS HOME JS Introduction JS Where To JS Output JS Statements JS Syntax JS Comments JS Variables JS Operators JS Arithmetic Slime Running 2 Silver Saucony ISO Blue Shoes Zealot Men's xq71I0 JS Data Types JS Functions JS Objects JS Events JS Strings JS String Methods JS Numbers JS Number Methods JS Arrays JS Array Methods JS Array Sort JS Array Iteration JS Dates JS Date Formats JS Date Get Methods JS Date Set Methods JS Math JS Random JS Booleans JS Comparisons JS Conditions JS Switch Mens Blue Running One One Lavender Arahi Medieval Hoka Shoe wTzq7Uf Black Slippers Opera Tamarac by International Men's UAwXxxzFq JS Break JS Type Conversion JS Bitwise JS RegExp JS Errors JS Scope JS Hoisting JS Strict Mode JS this Keyword JS Let JS Const JS Debugging JS Style Guide JS Best Practices JS Mistakes JS Performance JS Reserved Words JS Versions JS Version ES5 JS Version ES6 JS JSON

JS Forms

JS Forms Forms API

JS Objects

Object Definitions Object Properties Object Methods Object Accessors Object Constructors Object Prototypes Object ECMAScript 5

JS Functions

Function Definitions Function Parameters Function Invocation Function Call Men Exercise Women Swim Aqua Surf Shoes Barefoot Fins Beach Yoga Durable Pool Socks Water eleganceoo White xpq5dgw6x Function Closures

Top Shoe Low Heathrow DC SE Navy JS HTML DOM

DOM Intro DOM Methods DOM Document DOM Elements DOM HTML DOM CSS DOM Animations DOM Events DOM Event Listener DOM Navigation DOM Nodes DOM Collections DOM Node Lists

JS Browser BOM

JS Window JS Screen JS Location JS History JS Navigator JS Popup Alert JS Timing JS Cookies


AJAX Intro AJAX XMLHttp White Men's Originals adidas Gum Black PEq77xO AJAX Response AJAX XML File AJAX PHP AJAX ASP AJAX Database AJAX Applications AJAX Examples


JSON Intro JSON Syntax JSON vs XML JSON Data Types JSON Parse JSON Stringify JSON Objects JSON Arrays JSON PHP JSON HTML Extension Brown Men's Industrial Caterpillar Shoe vqSxw4WU

JS Examples

JS Examples JS HTML DOM JS HTML Input JS HTML Objects JS HTML Events JS Browser JS Quiz JS Certificate

JS References

JavaScript Objects HTML DOM Objects

Low Navy Heathrow Shoe DC Top SE zZxEwnq8

A JavaScript function is a block of code designed to perform a particular task.

A JavaScript function is executed when "something" invokes it (calls it).


function myFunction(p1, p2) {
    return p1 * p2;              // The function returns the product of p1 and p2
Pump Hannah Slide Chestnut Women's Eastland qZtg66
Try it Yourself »

Low SE Shoe Heathrow DC Top Navy

JavaScript Function Syntax

A JavaScript function is defined with the function keyword, followed by a name, followed by parentheses ().

Function names can contain letters, digits, underscores, and dollar signs (same rules as variables).

The parentheses may include parameter names separated by commas:
(parameter1, parameter2, ...)

The code to be executed, by the function, is placed inside curly brackets: {}

function name(parameter1, parameter2, parameter3) {
    code to be executed

Function Navy SE DC Low Shoe Heathrow Top parameters are listed inside the parentheses () in the function definition.

Function arguments are the values received by the function when it is invoked.

Navy Shoe SE Heathrow Top Low DC Inside the function, the arguments (the parameters) behave as local variables.

A Function is much the same as a Procedure or a Subroutine, in other programming languages.

Function Invocation

The code inside the function will execute when "something" invokes (calls) the function:

  • When an event occurs (when a user clicks a button)
  • When it is invoked (called) from JavaScript code
  • Automatically (self invoked)

You will learn a lot more about function invocation later in this tutorial.

Function Return

When JavaScript reaches a DC Navy Heathrow Top Low SE Shoe return statement, the function will stop executing.

If the function was invoked from a statement, JavaScript will "return" to execute the code after the invoking statement.

Functions often compute a return value. The return value is "returned" back to the "caller":


Calculate the product of two numbers, and return the result:

var x = myFunction(4, 3);    // Function is called, return value will end up in x

function myFunction(a, b) {
    return a * b;            // Function returns the product of a and b

The result in x will be:

Try it Yourself »

Why Functions?

You can reuse code: Define the code once, and use it many times.

You can use the same code many times with different arguments, to produce different results.


Convert Fahrenheit to Celsius:

function toCelsius(fahrenheit) {
    return (5/9) * (fahrenheit-32);
document.getElementById("demo").innerHTML = toCelsius(77);
Try it Yourself »

The () Operator Invokes the Function

Using the example above, toCelsius refers to the function object, and toCelsius() refers to the function result.

Accessing a function without () will return the function definition instead of the function result:


function toCelsius(fahrenheit) {
    return (5/9) * (fahrenheit-32);
document.getElementById("demo").innerHTML = toCelsius;
Try it Yourself »

Functions Used as Variable Values

Functions can be used the same way as you use variables, in all types of formulas, assignments, and calculations.


Instead of using a variable to store the return value of a function:

var x = toCelsius(77);
var text = "The temperature is " + x + SE Top DC Heathrow Low Navy Shoe SE Top Heathrow Shoe DC Navy Low " Celsius";

You can use the function directly, as a variable value:

var text = "The temperature is " + toCelsius(77) + " Celsius";
Try it Yourself »

You will learn a lot more about functions later in this tutorial.

Local Variables

Variables declared within a JavaScript function, become LOCAL to the function.

Local variables can only be accessed from within the function.


// code here can NOT use carName

function myFunction() {
    var carName = "Volvo";
    // code here CAN use carName

// code here can NOT use carName
Try it Yourself »

Since local variables are only recognized inside their functions, variables with the same name can be used in different functions.

Local variables are created when a function starts, and deleted when the function is completed.

Test Yourself with Exercises!

Exercise 1 »   Exercise 2 »   Exercise 3 »   Exercise 4 »   Exercise 5 »