Simple function called

greeting

that shows the following message:

Hello, my name is john

using

alert

built-in function. Then we can call the function by typing the function name followed by parenthesis:

greeting();

function greeting() {
    alert('Hello, my name is john');
}
greeting();

The same function with more flexibility. We pass the parameter

name

to the function, so it can be called for different users. When we call the function, we need to pass a string, as an argument

greeting('John');

function greeting(name) {
    alert('Hello, my name is ' + name);
}
greeting('John');

The same function with several parameters. We added another parameter

age

to the function

function greeting(name, age) {
    alert('Hello, my name is ' + name + ' and I am ' + age + ' years old');
}
greeting('John', 25);

The following function returns value, so that we can use the function in expressions

function doubleMe(number) {
    return 2*number;
}
console.log(3*doubleMe(50));  // 300

We can assign default values to parameters if they are not passed when the function gets called

function aboutMe(profession = 'student', name, city = 'Tbilisi' ) {
    console.log('I am a ' + profession + ' from ' + city + ' and my name is ' + name);
}
aboutMe(undefined, 'Valeri');