[TIL#4]JavaScriptベース-2

Goal:JavaScriptの基本を学ぶ
Table of Contents
1.差異var、let、const2.JavaScriptデータ型
3.配列の運用

3.配列の運用

-アレイ宣言(Declaration)

const arr1 = new Array();
const arr2 = [1, 2];

- Index position

const fruits = ['🍎', '🍌'];
console.log(fruits);
console.log(fruits.length);
console.log(fruits[0]);
console.log(fruits[1]);
console.log(fruits[2]);
console.log(fruits[fruits.length - 1]);
console.clear();

-Looping over an array
print all fruits

for

for (let i = 0; i < fruits.length; i++) {
  console.log(fruits[i]);
}

for of

for (let fruit of fruits) {
  console.log(fruit);
}

forEach

fruits.forEach((fruit) => console.log(fruit));

-Addtion, deletion, copy

push: add an item to the end

fruits.push('🍓', '🍑');
console.log(fruits);

pop: remove an item from the end

const poped = fruits.pop();
fruits.pop();
console.log(fruits);

unshift: add an item to the benigging

fruits.unshift('🍓', '🍋');
console.log(fruits);

shift: remove an item from the benigging

fruits.shift();
fruits.shift();
console.log(fruits);

note!! shift, unshift are slower than pop, push
splice: remove an item by index position

fruits.push('🍓', '🍑', '🍋');
console.log(fruits);
fruits.splice(1, 1);
console.log(fruits);
fruits.splice(1, 0, '🍏', '🍉');
console.log(fruits);

combine two arrays

const fruits2 = ['🍐', '🥥'];
const newFruits = fruits.concat(fruits2);
console.log(newFruits);

-Searching

indexOf: find the index

console.clear();
console.log(fruits);
console.log(fruits.indexOf('🍎'));
console.log(fruits.indexOf('🍉'));
console.log(fruits.indexOf('🥥'));

- includes

console.log(fruits.includes('🍉'));
console.log(fruits.includes('🥥'));

- lastIndexOf

fruits.push('🍎');
console.log(fruits);
console.log(fruits.indexOf('🍎'));
console.log(fruits.lastIndexOf('🥥'));

注意:エリー