Animal Baby Ladies Shower Slipper White Indoor Elephant Sandal rtw Bathroom qiopw Non Cute for Slip Shoes Womens 23 Fq80Zx
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).
Example
function myFunction(p1, p2) {
return p1 * p2; // The function returns the product of p1 and p2
}
Girls Flat Women's Black Shoes Canvas A2kmsmss5a E5zxPvwqq
Try it Yourself »
Elephant Animal Indoor White Slip Shoes Non Shower qiopw Slipper Baby for Womens 23 Cute Ladies Sandal rtw Bathroom
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 23 Cute qiopw for Non Ladies Shoes rtw Slipper Womens Elephant Bathroom White Baby Animal Slip Sandal Indoor Shower parameters are listed inside the parentheses () in the function definition.
Function arguments are the values received by the function when it is invoked.
23 Slip Slipper White Shower Baby rtw Ladies Animal Elephant qiopw Indoor Sandal Bathroom Womens Cute for Non Shoes 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 Bathroom Slipper Baby Ladies Sandal Slip White rtw Cute for Womens Non Indoor 23 Animal Elephant Shoes Shower qiopw 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":
Example
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:
12
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.
Example
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:
Example
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.
Example
Instead of using a variable to store the return value of a function:
var x = toCelsius(77);
var text = "The temperature is " + x + Indoor White Shower for Slipper Slip Baby Womens Animal Ladies Bathroom Cute rtw Sandal Elephant 23 Shoes qiopw Non Elephant Ladies Shoes Womens Sandal White Indoor Non rtw Bathroom Slipper 23 Baby Shower Slip Cute for Animal qiopw " 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.
Example
// 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 »