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HTML

Array

          let arr = new Array();
let arr = [];
        

let fruits = ["Apple", "Orange", "Plum"];

let fruits = ["Apple", "Orange", "Plum"];

alert( fruits[0] ); // Apple
alert( fruits[1] ); // Orange
alert( fruits[2] ); // Plum

fruits[2] = 'Pear'; //  ["Apple", "Orange", "Pear"]

fruits[3] = 'Lemon'; //  ["Apple", "Orange", "Pear", "Lemon"]

length

let fruits = ["Apple", "Orange", "Plum"];

alert( fruits.length ); // 3

alert

let fruits = ["Apple", "Orange", "Plum"];

alert( fruits ); // Apple,Orange,Plum

// 
let arr = [ 'Apple', { name: 'John' }, true, function() { alert('hello'); } ];

//  1  name
alert( arr[1].name ); // John

//  3 
arr[3](); // hello

          let fruits = [
  "Apple",
  "Orange",
  "Plum",
];
        

at

JavaScript polyfills.

fruits[-1]

JavaScript undefined

fruits[fruits.length - 1]

let fruits = ["Apple", "Orange", "Plum"];

alert( fruits[fruits.length-1] ); // Plum

fruits.at(-1)

let fruits = ["Apple", "Orange", "Plum"];

//  fruits[fruits.length-1] 
alert( fruits.at(-1) ); // Plum

arr.at(i)

i >= 0 arr[i]
i

pop/push, shift/unshift

queue

push .
shift

[]

push .
pop .

[]

LIFOLast-In-First-Out FIFOFirst-In-First-Out

JavaScript //

deque

pop

let fruits = ["Apple", "Orange", "Pear"];

alert( fruits.pop() ); //  "Pear"  alert 

alert( fruits ); // Apple, Orange

fruits.pop() fruits.at(-1) fruits.pop()

push

let fruits = ["Apple", "Orange"];

fruits.push("Pear");

alert( fruits ); // Apple, Orange, Pear

fruits.push(...) fruits[fruits.length] = ...

shift

let fruits = ["Apple", "Orange", "Pear"];

alert( fruits.shift() ); //  Apple  alert 

alert( fruits ); // Orange, Pear

unshift

let fruits = ["Orange", "Pear"];

fruits.unshift('Apple');

alert( fruits ); // Apple, Orange, Pear

push unshift

let fruits = ["Apple"];

fruits.push("Orange", "Peach");
fruits.unshift("Pineapple", "Lemon");

// ["Pineapple", "Lemon", "Apple", "Orange", "Peach"]
alert( fruits );

arr[0] obj[key] arr key

length

JavaScript 8

let fruits = ["Banana"]

let arr = fruits; //  ()

alert( arr === fruits ); // true

arr.push("Pear"); // 

alert( fruits ); // Banana, Pear   2

JavaScript

          let fruits = []; // 

fruits[99999] = 5; // 

fruits.age = 25; //

Javascript

arr.test = 5
arr[0] arr[1000] ()
arr[1000]arr[999]

JavaScript {}

push/pop shift/unshift

[]

fruits.shift(); //

0

shift :

0
1 02 1
length

[]

unshift

push/pop pop length

pop

fruits.pop(); //

[]

pop pop

push

for

let arr = ["Apple", "Orange", "Pear"];

for (let i = 0; i < arr.length; i++) {
  alert( arr[i] );
}

for..of

let fruits = ["Apple", "Orange", "Plum"];

// 
for (let fruit of fruits) {
  alert( fruit );
}

for..of

for..in

let arr = ["Apple", "Orange", "Pear"];

for (let key in arr) {
  alert( arr[key] ); // Apple, Orange, Pear
}

for..in

length for..in
for..in 10-100

for..in

length

length

let fruits = [];
fruits[123] = "Apple";

alert( fruits.length ); // 124

length

let arr = [1, 2, 3, 4, 5];

arr.length = 2; //  2 
alert( arr ); // [1, 2]

arr.length = 5; //  length 
alert( arr[3] ); // undefined

arr.length = 0;

new Array()

let arr = new Array("Apple", "Pear", "etc");

[]

new Array

let arr = new Array(2); //  [2] 

alert( arr[0] ); // undefined

alert( arr.length ); // length 2

let matrix = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9]
];

alert( matrix[1][1] ); //

toString

toString

let arr = [1, 2, 3];

alert( arr ); // 1,2,3
alert( String(arr) === '1,2,3' ); // true

alert( [] + 1 ); // "1"
alert( [1] + 1 ); // "11"
alert( [1,2] + 1 ); // "1,21"

Symbol.toPrimitive valueOf toString [] [1] "1"[1,2] "1,2"

"+"

alert( "" + 1 ); // "1"
alert( "1" + 1 ); // "11"
alert( "1,2" + 1 ); // "1,21"

==

JavaScript == JavaScript

==
==
null undefined ==

===

==

alert( [] == [] ); // false
alert( [0] == [0] ); // false

==

alert( 0 == [] ); // true

alert('0' == [] ); // false

[] ''

//  []  '' 
alert( 0 == '' ); // true ''  0

alert('0' == '' ); // false

==

          //  ()
let arr = [item1, item2...];

// new Array ()
let arr = new Array(item1, item2...);
        

new Array(number)

length
length

arr[0]
at(i) i i >= 0 arr[i]

push(...items) items
pop()
shift()
unshift(...items) items

for (let i=0; i<arr.length; i++)
for (let item of arr) items
for (let i in arr)

== > <

for..of

?

          let fruits = ["Apples", "Pear", "Orange"];

//  push 
let shoppingCart = fruits;
shoppingCart.push("Banana");

// fruits 
alert( fruits.length ); // ?
        

4:

let fruits = ["Apples", "Pear", "Orange"];

let shoppingCart = fruits;

shoppingCart.push("Banana");

alert( fruits.length ); // 4

shoppingCart fruits

styles Jazz Blues
Rock-n-Roll
Classics
Rap Reggae

          Jazz, Blues
Jazz, Blues, Rock-n-Roll
Jazz, Classics, Rock-n-Roll
Classics, Rock-n-Roll
Rap, Reggae, Classics, Rock-n-Roll
        

let styles = ["Jazz", "Blues"];
styles.push("Rock-n-Roll");
styles[Math.floor((styles.length - 1) / 2)] = "Classics";
alert( styles.shift() );
styles.unshift("Rap", "Reggae");

          let arr = ["a", "b"];

arr.push(function() {
  alert( this );
});

arr[2](); // ?
        

arr[2]() obj[method]() obj arr method 2

arr[2] this arr

let arr = ["a", "b"];

arr.push(function() {
  alert( this );
})

arr[2](); // a,b,function(){...}

sumInput()

prompt

P.S. 0 0

demo

prompt value value = +value 0

function sumInput() {

  let numbers = [];

  while (true) {

    let value = prompt("A number please?", 0);

    // 
    if (value === "" || value === null || !isFinite(value)) break;

    numbers.push(+value);
  }

  let sum = 0;
  for (let number of numbers) {
    sum += number;
  }
  return sum;
}

alert( sumInput() );

arr = [1, -2, 3, 4, -9, 6].

arr

getMaxSubSum(arr)

          getMaxSubSum([-1, 2, 3, -9]) == 5
getMaxSubSum([2, -1, 2, 3, -9]) == 6
getMaxSubSum([-1, 2, 3, -9, 11]) == 11
getMaxSubSum([-2, -1, 1, 2]) == 3
getMaxSubSum([100, -9, 2, -3, 5]) == 100
getMaxSubSum([1, 2, 3]) == 6
        

getMaxSubSum([-1, -2, -3]) = 0

O(n2) O(n)

[-1, 2, 3, -9, 11]

          //  -1 
-1
-1 + 2
-1 + 2 + 3
-1 + 2 + 3 + (-9)
-1 + 2 + 3 + (-9) + 11

//  2 
2
2 + 3
2 + 3 + (-9)
2 + 3 + (-9) + 11

//  3 
3
3 + (-9)
3 + (-9) + 11

//  -9 
-9
-9 + 11

//  11 
11
        

function getMaxSubSum(arr) {
  let maxSum = 0; //  0

  for (let i = 0; i < arr.length; i++) {
    let sumFixedStart = 0;
    for (let j = i; j < arr.length; j++) {
      sumFixedStart += arr[j];
      maxSum = Math.max(maxSum, sumFixedStart);
    }
  }

  return maxSum;
}

alert( getMaxSubSum([-1, 2, 3, -9]) ); // 5
alert( getMaxSubSum([-1, 2, 3, -9, 11]) ); // 11
alert( getMaxSubSum([-2, -1, 1, 2]) ); // 3
alert( getMaxSubSum([1, 2, 3]) ); // 6
alert( getMaxSubSum([100, -9, 2, -3, 5]) ); // 100

O(n2) 2 4

100010000

s s s=0 s

function getMaxSubSum(arr) {
  let maxSum = 0;
  let partialSum = 0;

  for (let item of arr) { // arr  item
    partialSum += item; //  partialSum
    maxSum = Math.max(maxSum, partialSum); // 
    if (partialSum < 0) partialSum = 0; //  0
  }

  return maxSum;
}

alert( getMaxSubSum([-1, 2, 3, -9]) ); // 5
alert( getMaxSubSum([-1, 2, 3, -9, 11]) ); // 11
alert( getMaxSubSum([-2, -1, 1, 2]) ); // 3
alert( getMaxSubSum([100, -9, 2, -3, 5]) ); // 100
alert( getMaxSubSum([1, 2, 3]) ); // 6
alert( getMaxSubSum([-1, -2, -3]) ); // 0

1 O(n)

          function getMaxSubSum(arr) {
  let maxSum = 0;
  let partialSum = 0;

  for (let item of arr) {
    partialSum += item;
    maxSum = Math.max(maxSum, partialSum);
    if (partialSum < 0) partialSum = 0;
  }
  return maxSum;
}
        