Home - News ( United States | United Kingdom | Italy | Germany ) - Football scores

Showing content from https://www.w3schools.com/js/js_functions.asp below:

Website Navigation

• Tutorials
• Exercises
• Certificates
• Services

JavaScript Functions

Functions are fundamental building blocks in all programming.

Functions enable better code organization, modularity, and efficiency.

Functions are reusable block of code designed to perform a particular task.

Functions execute when they are "called" or "invoked".

Function to compute the product of two numbers:

function myFunction(p1, p2) {
  return p1 * p2;
}

function name(p1, p2, p3) { // code }

A function is defined with the function keyword, followed by the function name, followed by parentheses ( ), followed by brackets { }.

The name follows the naming rules for variables (letters, digits, ...).

Optional parameters are listed inside parentheses: (p1, p2, p3)

The code to be executed is listed inside curly brackets: { code }

Functions can optionally return a value back to the "caller".

With functions you can reuse code

You can write code that can be used many times.

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

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

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

The () operator invokes (calls) the function:

Convert Fahrenheit to Celsius:

function toCelsius(fahrenheit) {

return (5/9) * (fahrenheit-32);

}

let value = toCelsius(77);

Accessing a function with incorrect parameters can return an incorrect answer:

function toCelsius(fahrenheit) {

return (5/9) * (fahrenheit-32);

}

let value = toCelsius();

Accessing a function without () returns the function and not the function result:

function toCelsius(fahrenheit) {

return (5/9) * (fahrenheit-32);

}

let value = toCelsius;

In the examples above, toCelsius refers to the function object, and toCelsius() refers to the function result.

Arrow functions were introduced in ES6.

Arrow functions allow us to write shorter function syntax:

Function to compute the product of a and b

let myFunction = function(a, b) {return a * b}

Try it Yourself »

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() {

let carName = "Volvo";

// code here CAN use carName

}

// code here can NOT use carName

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.

In JavaScript, function parameters and arguments are distinct concepts:

Parameters are the names listed in the function definition.

Parameters are the names of the values that will be passed.

"name" and "age" are parameters:

function greet(name, age) {
  return `Hello $name! You are ${age} years old.`;
}

Arguments are the values passed to the function when it is invoked or called.

Arguments are the values received by the function.

Functions can be used as variables, in all types of formulas, assignments, and calculations.

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

let x = toCelsius(77);
let text = "The temperature is " + x + " Celsius";

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

let text = "The temperature is " + toCelsius(77) + " Celsius";

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

Track your progress - it's free!

RetroSearch is an open source project built by @garambo | Open a GitHub Issue

Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo

HTML: 3.2 | Encoding: UTF-8 | Version: 0.7.4