Mapping JS

Declare

const testMap = new Map()

set map

testMap.set(1,{name:"boris",cash:345});

testMap.set(2,{name:"tony",cash:45});

testMap.set(3,{name:"peter",cash:5});

Map {1 => Object {name: "boris", cash: 345}, 2 => Object {name: "tony", cash: 45}, 3 => Object {name: "peter", cash: 5}}

properties

testMap.size

3

testMap.has(2)

true

testMap.has(56)

false

methods

testMap.get(3).name

"peter"

for loop

//first item in array is key and second is value

for(let item of testMap){ console.log( item[1].cash)}//value

345

45

5

for(let item of testMap.keys()){ console.log( item)}

1

2

3

Array methods

Using splice to add items in any position

const arr = ['a','b','c','d']

x = arr.splice(2,0,'3')

x will be empty - []

arr will be ["a", "b", "3", "c", "d"]

Add to the beginning of array

arr.unshift(-13)

[-13, "a", "b", "3", "c", "d"]

remove 1^st item

arr.shift()

["a", "b", "3", "c", "d"]

For Each

var temp =””

arr.forEach(function (item) {

    if (isNaN(item)) {

        temp += item;

    }

});

temp = "abcd"

mapping

const test =[{name:"herby",cash:23},{name:"boris",cash:456} ]

const cash = test.map(x=>x.cash)

cash = [23, 456]

Every and Some

const test2 =[{name:"herby",cash:23,eyecolor:"brown"},{name:"boris",cash:456} ]

test2.some(x=>x.eyecolor)

true

test2.every(x=>x.eyecolor)

false

Find

returns 1^st item

const z = test2.find(x=>{return x.eyecolor === "brown"})

z    {name:"herby",cash:23,eyecolor:"brown"}

const w = test2.find(x=>{return x.cash  > 0})

w   {name:"herby",cash:23,eyecolor:"brown"}

to get multiple items as an array use:

Filter

const t = test2.filter(x=>{return x.cash  > 0})

sort

 ascending

test2.sort((x,z)=>x.cash -z.cash)

descending

test2.sort((x,z)=>z.cash -x.cash)

Aggregating

console.log(test2.reduce((a,c)=>a+=c.cash,0))

479

why is 32 bit x86

here

New Parameter Functionality in JS

1. New Parameter Functionality
   
   Rest Params
   
   function testParams( i , ...j){
   var total = 0;
   j.forEach( function(value, index) { total += value; });
   return Math.pow(total,i);
   }
   testParams(2,1,2,3,4)
   100
   
   Rest Params with Arrow Functions
   function testParams( i , ...j){
   var total = 0;
   j.forEach( value => total += value);
   return Math.pow(total,i);
   
   }
   testParams(2,1,2,3,4)
   100
   
   default Params
   
   function testDefault(i, power =2){
   return Math.pow(i,power );
   }
   
   testDefault(10)
   100
   testDefault(10,3)
   1000

access list boxes - stop selection

use Locked property


if you use the enabled property then the scrollbars wont work

const in js

1. new const feature
   
   in the past there was no real constants in js, everything could be overwritten (even sometimes keywords)
   in ECMAScript6 this has been alleviated
   
   const in JS means the object can be assigned once
   if you try this
   
   const i = 45
   i= 0
   console.log(I)
   
   
   this will fail
   SyntaxError: Identifier 'i' has already been declared
   
   with objects member can be assigned afterwards
   
   
   const obj2 = {}
   obj2.a ="gg"
   
   
   
   but subsequent
   obj2 = {}
   will fail
   
   even with const, the only way to have a readonly member of an object is
   
   var testobj = {};
   Object.defineProperty( testobj , "pseudoconst",
   {
   value: 3,
   
   writable: false,
   
   enumerable: true,
   
   configurable: true
   });
   
   testobj.pseudoconst
   3
   testobj.pseudoconst = 5//this wont raise an error but wont change the value either
   5
   testobj.pseudoconst
   3
   
   

let in js

1. as Douglas Crockford has said, the worst feature of JavaScript is global variables.
   This has been alleviated greatly by block scoped variables
   
   consider the following
   
   
   var test ="herman"
   
   {
   test ="boris";
   console.log(test)
   }
   console.log(test)
   
   or
   
   
   var test ="herman"
   
   {
   var test ="boris";
   console.log(test)
   }
   console.log(test)
   
   the result will be
   
   
   boris
   boris
   
   However, with the new let keyword
   
   var test ="herman"
   
   {
   let test ="boris";
   console.log(test)
   }
   console.log(test)
   
   the results are now
   boris
   herman