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                // 2番目の要素から2つ取り除く
const arr = ['one', 'two', 'three', 'four'];
let len = arr.splice(1, 2);
console.log(arr); // ["one","four"]
console.log(len); // ["two","three"]

// 2番目の要素から1つも取り除かず、'ten'を追加
const arr2 = ['one', 'two', 'three', 'four'];
let len2 = arr2.splice(1, 0, 'ten');
console.log(arr2); // ["one","ten","two","three","four"]
console.log(len2); // []

// 2番目の要素から1つ取り除ぞいて、'ten', 100を追加
const arr3 = ['one', 'two', 'three', 'four'];
let len3 = arr3.splice(1, 1, 'ten',100);
console.log(arr3); // ["one","ten",100,"three","four"]
console.log(len3); // ["two"]

// deleteCount 引数が省略された場合、start 以降のすべての要素が取り除かれます。
const arr4 = ['one', 'two', 'three', 'four'];
let len4 = arr4.splice(1);
console.log(arr4); // ["one"]
console.log(len4); // ["two","three","four"]