What are functions in JavaScript: Beginners

What are functions in JavaScript: Beginners

·

3 min read

In this section, we cover functions, what they are utilized for and how to keep in touch with them. A function is a way to encapsulate a portion of your code so a specific action can e reused and called on to run at a specific time.


Declaration

An example of what the syntax to declare a function looks like.

function name (parameterrs) {
    // function body goes here
}

// example
function showMessage() {
    alert("hello world"); 
}

Note: A parameter is a named variable passed into a function while function arguments are the actual values assigned to the parameters.

Naming

Since the 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(); 
//calculted a 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(Args) which act as a variable within the function. This allows for better reusability.

function calcAge(currentYear, birthYear) {
    return currentYeay - birthYear; 
}
const rahAge = calcAge(2021, 2004); 
// output: 17

const samAge = calcAge(2021, 2000); 
// Output:21

Local variable

A variable declared inside a function will only be visible within the scope of the function.

function showMessage() {
    let message = "Hello World"; 
    // local variable

    alert(message); 
}

showMessage(); 
// Hello World

alert(message); // error
// the 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 = 10; 

function checkAge(age) {
    if (age >= movieAgeLimit) {
        return true; 
    } else {
        return false; 
    }
    // alternative: return age >= moveAgeLimit 
}

const hasAccess = checkAge(18); 
if (hasAccess) {
    alert("enjoy the movie"); 
} else {
    alert("Get out please!"); 
}

Call another function

It can be also used to perform an action or call another function.

const yourName = prompt("What is your name? "); 

function showWelcomeMessage(name) {
    alert(`Welcome ${name}`); 
}

showWelcomeMessage(yourName);

👓Wrapping

Function names tend to be verbs to easily describe what the function does. Arguments are values you can pass to be used within a function. Variables declared within a function are only visible within the function scope. A scope can return a value or call another function / action. Use functions to store re-usable code that can be called as and when needed.

Thank you For reading ⚡


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