Null合体演算子
2020-08-14
Null合体演算子
しらなかったのでメモ
よくあるデフォルト値を代入するときなどに使うやつ
||との違い
||
左辺がfalsyな値なら右辺を返す
falsyな値とはnull,undefined,0と空文字列など
??
左辺がnullまたはundefinedの場合に右の値を返す
0や空文字列の場合はそちらを返したい場合などに有効
実行例
??
const value1 = null ?? 'default string';
console.log(value1);
// expected output: "default string"
const value2 = undefined ?? 'default string';
console.log(value2);
// expected output: "default string"
const value3 = "" ?? "default string";
console.log(value3);
// expected output: ""
const value4 = 0 ?? 42;
console.log(value4);
// expected output: 0
const value5 = [] ?? [1,2,3];
console.log(value5);
// expected output: []
const value6 = {} ?? "{a: 'b'}"
console.log(value6);
// expected output: {}||
const value1 = null || 'default string';
console.log(value1);
// expected output: "default string"
const value2 = undefined || 'default string';
console.log(value2);
// expected output: "default string"
const value3 = "" || "default string";
console.log(value3);
// expected output: "default string"
const value4 = 0 || 42;
console.log(value4);
// expected output: 42
const value5 = [] || [1,2,3];
console.log(value5);
// expected output: []
const value6 = {} || "{a: 'b'}"
console.log(value6);
// expected output: {}
