JS의 Array 객체의 일부 작동 방법에 대한 간략한 분석(코드 포함)

console.log(Array.from("foo"));
// expected output: Array ["f", "o", "o"]
console.log(Array.from([1, 2, 3], (x) => x + x));
// expected output: Array [2, 4, 6]

Array.isArray([1, 2, 3]);
// true
Array.isArray({ foo: 123 });
// false
Array.isArray("foobar");
// false
Array.isArray(undefined);
// false

Array.of(7); // [7]
Array.of(1, 2, 3); // [1, 2, 3]

Array(7); // [ , , , , , , ]
Array(1, 2, 3); // [1, 2, 3]
//es5
if (!Array.of) {
  Array.of = function () {
    return Array.prototype.slice.call(arguments);
  };
}

var array1 = ["a", "b", "c"];
var array2 = ["d", "e", "f"];

console.log(array1.concat(array2));
// expected output: Array ["a", "b", "c", "d", "e", "f"]

var array1 = [1, 2, 3, 4, 5];

// place at position 0 the element between position 3 and 4
console.log(array1.copyWithin(0, 3, 4));
// expected output: Array [4, 2, 3, 4, 5]

// place at position 1 the elements after position 3
console.log(array1.copyWithin(1, 3));
// expected output: Array [4, 4, 5, 4, 5]

var array1 = ["a", "b", "c"];

var iterator1 = array1.entries();

console.log(iterator1.next().value);
// expected output: Array [0, "a"]

console.log(iterator1.next().value);
// expected output: Array [1, "b"]

var array1 = [1, 30, 39, 29, 10, 13];
console.log(array1.every((x) => x < 40));
//out true

var array1 = [1, 2, 3, 4];
// fill with 0 from position 2 until position 4
console.log(array1.fill(0, 2, 4));
// expected output: [1, 2, 0, 0]
// fill with 5 from position 1
console.log(array1.fill(5, 1));
// expected output: [1, 5, 5, 5]
console.log(array1.fill(6));
// expected output: [6, 6, 6, 6]

var words = ["spray", "limit", "elite", "exuberant", "destruction", "present"];

const result = words.filter((word) => word.length > 6);

console.log(result);
// expected output: Array ["exuberant", "destruction", "present"]

var array1 = [5, 12, 8, 130, 44];

var found = array1.find((x) => x > 10);

console.log(found);
// expected output: 12

var array1 = [5, 12, 8, 130, 44];

var index = array1.findIndex((x) => x > 10);

console.log(index);
// expected output: 1

var arr1 = [1, 2, [3, 4]];
arr1.flat();
// [1, 2, 3, 4]

var arr2 = [1, 2, [3, 4, [5, 6]]];
arr2.flat();
// [1, 2, 3, 4, [5, 6]]

var arr3 = [1, 2, [3, 4, [5, 6]]];
arr3.flat(2);
// [1, 2, 3, 4, 5, 6]
var arr4 = [1, 2, , 4, 5];
arr4.flat();
// [1, 2, 4, 5]

var arr1 = [1, 2, 3, 4];

arr1.map((x) => [x * 2]);
// [[2], [4], [6], [8]]

arr1.flatMap((x) => [x * 2]);
// [2, 4, 6, 8]

// only one level is flattened
arr1.flatMap((x) => [[x * 2]]);
// [[2], [4], [6], [8]]

var array1 = ["a", "b", "c"];

array1.forEach((value, index, arr) => console.log(value));
// output 'a'
// output 'b'
// output 'c'

var array1 = [1, 2, 3];

console.log(array1.includes(2));
// expected output: true

var pets = ["cat", "dog", "bat"];

console.log(pets.includes("cat"));
// expected output: true

console.log(pets.includes("at"));
// expected output: false

/var beasts = ['ant', 'bison', 'camel', 'duck', 'bison'];

console.log(beasts.indexOf('bison'));
// expected output: 1

// start from index 2
console.log(beasts.indexOf('bison', 2));
// expected output: 4

console.log(beasts.indexOf('giraffe'));
// expected output: -1

var elements = ["Fire", "Wind", "Rain"];

console.log(elements.join());
// expected output: Fire,Wind,Rain

console.log(elements.join(""));
// expected output: FireWindRain

console.log(elements.join("-"));
// expected output: Fire-Wind-Rain

//数组[1,2,3,3,4,5]求和
eval([1, 2, 3, 3, 4, 5].join("+")) = 18;

var array1 = ["a", "b", "c"];
var iterator = array1.keys();

for (let key of iterator) {
  console.log(key); // expected output: 0 1 2
}

var animals = ["Dodo", "Tiger", "Penguin", "Dodo"];

console.log(animals.lastIndexOf("Dodo"));
// expected output: 3

console.log(animals.lastIndexOf("Tiger"));
// expected output: 1

var array1 = [1, 4, 9, 16];

// pass a function to map
const map1 = array1.map((x) => x * 2);

console.log(map1);
// expected output: Array [2, 8, 18, 32]

var plants = ["broccoli", "cauliflower", "cabbage", "kale", "tomato"];
console.log(plants.pop());
// expected output: "tomato"
console.log(plants);
// expected output: Array ["broccoli", "cauliflower", "cabbage", "kale"]
plants.pop();
console.log(plants);
// expected output: Array ["broccoli", "cauliflower", "cabbage"]

var animals = ["pigs", "goats", "sheep"];

console.log(animals.push("cows"));
// expected output: 4

console.log(animals);
// expected output: Array ["pigs", "goats", "sheep", "cows"]

animals.push("chickens");

console.log(animals);
// expected output: Array ["pigs", "goats", "sheep", "cows", "chickens"]

const array1 = [1, 2, 3, 4];
const reducer = (accumulator, currentValue) => accumulator + currentValue;

// 1 + 2 + 3 + 4
console.log(array1.reduce(reducer));
// expected output: 10

// 5 + 1 + 2 + 3 + 4
console.log(array1.reduce(reducer, 5));
// expected output: 15

const array1 = [
  [0, 1],
  [2, 3],
  [4, 5],
].reduceRight((accumulator, currentValue) => accumulator.concat(currentValue));

console.log(array1);
// expected output: Array [4, 5, 2, 3, 0, 1]

var array1 = ["one", "two", "three"];
console.log("array1: ", array1);
// expected output: Array ['one', 'two', 'three']

var reversed = array1.reverse();
console.log("reversed: ", reversed);
// expected output: Array ['three', 'two', 'one']

/* Careful: reverse is destructive. It also changes
the original array */

console.log("array1: ", array1);
// expected output: Array ['three', 'two', 'one']

var array1 = [1, 2, 3];

var firstElement = array1.shift();

console.log(array1);
// expected output: Array [2, 3]

console.log(firstElement);
// expected output: 1

var animals = ["ant", "bison", "camel", "duck", "elephant"];

console.log(animals.slice(2));
// expected output: Array ["camel", "duck", "elephant"]

console.log(animals.slice(2, 4));
// expected output: Array ["camel", "duck"]

console.log(animals.slice(1, 5));
// expected output: Array ["bison", "camel", "duck", "elephant"]