`??=`という演算子であり、左辺が[[Nullish (JavaScript)|Nullish]]の場合にのみ右辺の値を代入する。 ```ts let a = "hoge" let b = null let c = undefined let d = "" a ??= "new" b ??= "new" c ??= "new" d ??= "new" console.log(a, b, c, d) // "hoge", "new", "new", "" ``` <button class="playground"><a href="https://www.typescriptlang.org/play?#code/DYUwLgBAhhC8ECIAWB7A5iBAoUkBGcEAdgK7DA7gQDGhJRAJiAGYCWRIDlkDhC2WGAH4h8BBwDu2AiLGTstWYnlZeS8SClYs1FEQDOKUADpg6ABRQANBDw3qNhgEosAeleJUGBDY1Tf8r4IQA">Playground</a></button>