久しぶりにArray.splice()を使って混乱した事 - Qiita

let array = []; array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 0]; array.splice(0, 1); console.log(array); // [2, 3, 4, 5, 6, 7, 8, 9, 0]; array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 0]; array.splice(0, 4); console.log(array); // [5, 6, 7, 8, 9, 0]; array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 0]; array.splice(4, 1); console.log(array); // [1, 2, 3, 4, 6, 7, 8, 9, 0]; array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 0]; array.splice(4, 4