This content originally appeared on DEV Community and was authored by Danish Saleem
Another chapter in the JavaScript for beginners’ series! In this chapter we cover functions, what they are used for and how to write them.
Functions
A function is a way to encapsulate a portion of your code so a specific action can be reused and called on to run at a specific time.
Declaration
An example of what the syntax to declare a function looks like.
function showMessage() {
alert("Hello World!");
}
showMessage();
Naming
Since functions are actions their name is usually a verb. Keep the names brief but accurate to describe what the function does.
showMessage(); // Shows a message
getAge(); // Returns the age
calcSum(); // Calculates the sum and returns the result
createForm(); // Creates and returns a form
checkPermission(); // Check a permission, returns true/false
Arguments
A function can require you to pass some arguments (agrs) which act as variable within the function. This allows for better reusability.
function calcAge(currentYear, birthYear) {
return currentYear - birthYear;
}
const myAge = calcAge(2021, 1989); // Output: 32
const johnAge = calcAge(2021, 1975); // Output: 46
Local Variables
A variable declared inside a function will only be visible within the function scope.
function showMessage() {
let message = "Hello World!"; // Local variable
alert(message);
}
showMessage(); // Output: Hello World!
alert(message); // Output: Error! - Variable is local to the function
Return a Value
A function can return a value - usually one generated or manipulated by the function code.
const movieAgeLimit = 13;
function checkAge(age) {
if (age >= movieAgeLimit) {
return true;
} else {
return false;
}
// Alternative: return age >= movieAgeLimit
}
const hasAccess = checkAge(18);
if (hasAccess) {
alert("Enjoy the movie");
} else {
alert("You are not old enough for this movie");
}
Call another Function
It can also be used to perform an action or call another function
const yourName = prompt("What is your name?");
function showWelcomeMessage(name) {
alert(`Welcome ${name}`);
}
showWelcomeMessage(yourName);
Summary
-
Functionnames tend to beverbsto easily describe what the function does. -
Argumentsare values you can pass to be used within a function. -
Local Variablesdeclared within afunctionare only visible within thefunctionscope. - A
functioncanreturnavalueor call anotherfunction / action. - Use
functionsto storereusablecode that can be called as and when needed.
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This content originally appeared on DEV Community and was authored by Danish Saleem
Danish Saleem | Sciencx (2021-12-11T08:28:28+00:00) JavaScript for Beginners – Chapter 7: Functions. Retrieved from https://www.scien.cx/2021/12/11/javascript-for-beginners-chapter-7-functions/
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