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<title>flat 与 flatMap</title>
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// flat 平
// 将多维数组转化为低维数组
const arr1 = [1, 2, 3, 4, [5, 6]];
console.log(arr1.flat()) // [1, 2, 3, 4, 5, 6]
const arr2 = [1, 2, 3, 4, [5, 6, [7, 8, 9]]];
// 参数为深度 是一个数字
console.log(arr2.flat(2)); // [1, 2, 3, 4, 5, 6, 7, 8, 9]
const arr3 = [1, 2, 3, 4, [5, 6, [7, [8, 9]]]];
console.log(arr3.flat(Infinity)); // [1, 2, 3, 4, 5, 6, 7, 8, 9]
// flatMap：结合了flat、map两步操作。
const arr4 = [1, 2, 3, 4];
const result = arr4.flatMap(item => [item * 10]);
console.log(result); // [10, 20, 30, 40]
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