安全に配列の一部要素を変更するメソッド。 ```js const xs = ["a", "i", "u"]; console.log(xs.with(1, "hoge")); // ["a", "hoge", "u"] console.log(xs); // ["a", "i", "u"] ``` <button class="playground"><a href="https://www.typescriptlang.org/play?target=99&ts=5.2.2#code/MYewdgzgLgBAHhGBeGBtARAQ3QGhugS13wFd0BdAbgFgAoUSEAGwFMA6JkAcwAoE2A7gSgALHgEY86EdxboAlPJq0A9CrRZi02VrLk6DCM3adeCJXTUbsUolL10gA">Playground</a></button>