chapter 6 Functional-light-js

c = console.log

//Primitive Immutability
// invalid, and also makes no sense
//2 = 2.5;


var x = 2;

x.length = 4;

x;              // 2
x.length;       // undefined


var x = new Number( 2 );

// works fine
x.length = 4;


var s = "hello";

s[1];               // "e"

s[1] = "E";
s.length = 10;

s;                  // "hello"


"use strict";

var s = new String( "hello" );

s[1] = "E";         // error
s.length = 10;      // error

s[42] = "?";        // OK

//c(s);                  // String {"hello", 42: "?"}


//Value to Value
function addValue(arr) {
    var newArr = [ ...arr, 4 ];
    return newArr;
}

addValue( [1,2,3] );    // [1,2,3,4]
function updateLastLogin(user) {
    var newUserRecord = Object.assign( {}, user );
    newUserRecord.lastLogin = Date.now();
    return newUserRecord;
}

var user = {
    lastLogin: 1
};
//c(user) //1
//updateLastLogin( user )
//c(user) //1
//c(updateLastLogin( user )) //Date.now()


//Non-Local
function foo(arh) {
  arh[0] = 5
}
var arr = [1,2,3];

foo( arr );

//console.log( arr[0] ); //5
//=>
arr = [1,2,3];

foo( [...arr] );         // ha! a copy!

//console.log( arr[0] );      // 1

var x = 0
{
  let  x = 1
  //c(x) //1
}
//c(x) //0


//Intent
var a = "420";
// later
a = Number( a );
// later
a = [ a ];
//If after changing from "420" to 420, the original "420" value is no longer needed, 
//then I think it's more readable to reassign a 
//rather than come up with a new variable name like aNum.


//It's Freezing in Here
var x = Object.freeze( [ 2, 3, [4, 5] ] );
// not allowed:
x[0] = 42;
// oops, still allowed:
x[2][0] = 42;

var arr = Object.freeze( [1,2,3] );

foo( arr );

//console.log( arr[0] );          // 1


//Performance
/*
var state = Immutable.List.of( 4, 6, 1, 1 );

var newState = state.set( 4, 2 );

state === newState;                 // false

state.get( 2 );                     // 1
state.get( 4 );                     // undefined

newState.get( 2 );                  // 1
newState.get( 4 );                  // 2

newState.toArray().slice( 2, 5 );   // [1,1,2]
*/


//