【JavaScript】スプレッド演算子

配列の展開

const value = [2, 3, 1, 4, 5];
console.log(Math.max(...value));

シャローコピー

// 配列の複製
let a = [1, 2, 3];
let b = [...a];
console.log(b); //[ 1, 2, 3 ]

// シャローコピーなので多次元配列やオブジェクト等は影響を受けてしまう
let c = [[1], [2], [3]];
let d = [...c];
c[0][0] = 0;
console.log(c); // [ [ 0 ], [ 2 ], [ 3 ] ]

配列の連結

let a = [0, 1, 2];
let b = [3, 4, 5];
let c = [...a, ...b];

console.log(c); // [ 0, 1, 2, 3, 4, 5 ]
a.push(...b);
console.log(a); // [ 0, 1, 2, 3, 4, 5 ]

配列の分割代入

let [a, ...other] = [1, 2, 3];
console.log(a, other); // 1 [ 2, 3 ]

iterableなオブジェクトを展開できる

String、NodeList、HTMLCollection等…

let sample = "sample";
console.log([...sample]); // [ 's', 'a', 'm', 'p', 'l', 'e' ]