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Array.prototype.flat()
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since 2020年1月.
flat() 函數以遞迴方式將特定深度的子陣列重新串接成為一新的陣列
嘗試一下
const arr1 = [0, 1, 2, [3, 4]];console.log(arr1.flat());// expected output: Array [0, 1, 2, 3, 4]const arr2 = [0, 1, [2, [3, [4, 5]]]];console.log(arr2.flat());// expected output: Array [0, 1, 2, Array [3, Array [4, 5]]]console.log(arr2.flat(2));// expected output: Array [0, 1, 2, 3, Array [4, 5]]console.log(arr2.flat(Infinity));// expected output: Array [0, 1, 2, 3, 4, 5]語法
js
var newArray = arr.flat([depth]);參數
depth選擇性指定巢狀陣列展開的深度。預設為 1。
回傳值
函數將會回傳一個由原先陣列的子陣列串接而成的新陣列。
範例
展開巢狀陣列
js
var arr1 = [1, 2, [3, 4]];arr1.flat();// [1, 2, 3, 4]var arr2 = [1, 2, [3, 4, [5, 6]]];arr2.flat();// [1, 2, 3, 4, [5, 6]]var arr3 = [1, 2, [3, 4, [5, 6]]];arr3.flat(2);// [1, 2, 3, 4, 5, 6]當遭遇空元素時
flat() 函數會自動清除陣列中空的元素
js
var arr4 = [1, 2, , 4, 5];arr4.flat();// [1, 2, 4, 5]替代方案
reduce 與concat
js
var arr1 = [1, 2, [3, 4]];arr1.flat();//展開單層陣列arr1.reduce((acc, val) => acc.concat(val), []); // [1, 2, 3, 4]js
//欲展開更深層的巢狀結構請使用reduce與concat的遞迴function flattenDeep(arr1) { return arr1.reduce( (acc, val) => Array.isArray(val) ? acc.concat(flattenDeep(val)) : acc.concat(val), [], );}flattenDeep(arr1); // [1, 2, 3, 1, 2, 3, 4, 2, 3, 4]js
//使用stack來實作非遞迴的展開var arr1 = [1, 2, 3, [1, 2, 3, 4, [2, 3, 4]]];function flatten(input) { const stack = [...input]; const res = []; while (stack.length) { // pop value from stack const next = stack.pop(); if (Array.isArray(next)) { // push back array items, won't modify the original input stack.push(...next); } else { res.push(next); } } //reverse to restore input order return res.reverse();}flatten(arr1); // [1, 2, 3, 1, 2, 3, 4, 2, 3, 4]js
// 递归版本的反嵌套function flatten(array) { var flattend = []; (function flat(array) { array.forEach(function (el) { if (Array.isArray(el)) flat(el); else flattend.push(el); }); })(array); return flattend;}規範
| Specification |
|---|
| ECMAScript® 2026 Language Specification # sec-array.prototype.flat |