JavaScript Functions

Function is a block of code designed to perform a specific task. We can reuse it whenever needed.

notes: function() first need to know return type

1.Function declaration

function greet()
{
console.log("hello world");
}
greet();  // hello world

2.Function with parameters/arguments

parameter - name/ input value , argument - value
Parameters receive values when the function is called.

function add(a, b){
console.log(a  +b);
}
add(10, 20);   //30

a and b are parameters. 10 and 20 arguments.

3.Function with return
return sends a value back to the caller(the value goes back to who calls).
reuse the result of another calculation.

function add(a, b){
return a + b;
}
let result = add(10,20);
console.log(result);  // 30

4.Default parameter
function without values are default parameter.

function greet(name = "world"){
console.log("hello" + name);
}
greet();
greet("sam");

output :
hello world
hello sam

5.Function expression
A function can stored in a variable.

let greet = function(){
console.log("hello");
};
greet();  //hello

6.Arrow function
A shorter way to write a function.

let add = (a, b) => {
return a + b;
};
console.log(add(5,3)); //8

//shorter version
let add = (a, b) => a + b;
console.log(add(5,3));  //8

7.Callback function
A callback is a function passed as an argument to another function.

function display(result){
console.log(result);
}

function add(a, b, callback){
callback(a + b);
}
add(10, 20, display);  // 30

notes:
normal function : perform a task and return the result.
callback function : passes a function to another function so it can decide when to call it. (used in button click, arrays, timers)

8.Function returning a value

function square(n){
return n * n;
}
console.log(square(5));   //25