in JavaScript, functions are objects, so there is actually no overloading, but we can do encapsulations like this

javascript-function-overloading.js

function greet(firstname, lastname, language) {
        
    language = language || 'en';
    
    if (language === 'en') {
        console.log('Hello ' + firstname + ' ' + lastname);   
    }
    
    if (language === 'es') {
        console.log('Hola ' + firstname + ' ' + lastname);   
    }
    
}

function greetEnglish(firstname, lastname) {
    greet(firstname, lastname, 'en');   
}

function greetSpanish(firstname, lastname) {
    greet(firstname, lastname, 'es');   
}

greetEnglish('John', 'Doe');
greetSpanish('John', 'Doe');