[TIL#4]JavaScriptベース-2

15449 ワード
loop 複文 整列 TIL array テキストリンク

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
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