Javascript: Functions (inbuilt function)

FUNCTIONS

A function is basic building block. In functional programming language, everything is done using functions. but pure function needed. a function is of two type: pure function and impure function. In pure function, it wont effect immutable and mutable function otherwise it will be impure function 

Example 1:
function hi(){
      console.log('I am inside hi');
}
hi() Example 2:
IIFE (immediately invoke functional expression)
()() Example 3:
(function(){
       console.log('I am anonymous function');
})(); 

Example 4:
function sendMail(option){  //mail send function
     console.log('Option is', option);
     var sinuna = option.email;
     var to = option.to;
     var santoo = option.sub;
     var text = option.msg;
     option.email = 'info@fascinating.com'
     return true;
     return 'string';
     return 4324;
     return null;
     return option;
}

var a = {
     email:'sinuna.chaudhary@gmail.com',
     to: 'santo.info@gmail.com',
     sub:'Request for leave',
    msg: 'Hello this is to request..'
}

var fnRes = sendMail(a);
console.log('function result', fnRes); 

Another Explanation:

Function is a reusable block of code to do certain task
Function declaration
() is known as paranthesis
var a;
a = function(){
var name = 'i am sinuna';
console.log('Hi inside', name); hi inside i am sinuna no scope outside block of code for name variable
};
a();
console.log('Hi outside', name) undefined

Reference error:
no value on reference
Best approach
function b(){
}
b();

Function type

1. named function
function my_name(){
}

2. unnamed function (Anonymous function: without name) mostly used
function(){
}

3. Function with return
function a(){
return
'hi'; 'hi' will not execute
}
var c = a();
After return, nothing will be executed.

Example: 
function with argument

Example 1: argument-> name
function sayHello(name){
    console.log('name >>', name);
}
console.log(sayHello('sinuna'));
Output: name>> sinuna
undefined, this function will return nothing

Example 2:Function with argument and return type
function sayHello(name){
console.log('name >>', name);
return ' welcome '+ name + ' to home';
}
console.log(sayHello('sinuna'));

Example 3: Function with multiple argument
function getName( name, address, phone){
console.log('name', name);
console.log('address', address);
console.log('phone', phone);
}
getName('sinuna', 'nepal', 123213);
getName(null, null, 123213)

Best approach: 

Multiple argument object
Object: a collection of properties
Function with multiple arguments

function getName( name, address, phone){
    console.log('name', name);
    console.log('address', address);
   console.log('phone', phone);
}
getName('sinuna', 'nepal', 123213);
getName(null, null, 123213)