javascript - "Array.from() does not create an intermediate array"是什么意思？

Question

来自MDN Web Docs , Array.from(obj, mapFn, thisArg) 与 Array.from(obj).map(mapFn, thisArg) 具有相同的结果， 只是它不创建中间数组。

This is especially important for certain array subclasses, like typed arrays, since the intermediate array would necessarily have values truncated to fit into the appropriate type.

“Array.from() 不会创建中间数组”是什么意思？

Answer 1

您可以将Array.from(obj).map(mapFn, thisArg)分解为

const arr1 = Array.from(obj);
const arr2 = arr1.map(mapFn, thisArg);

由于 Array.from() 和 Array.prototype.map 都返回一个新数组，因此已经创建了两个数组。

Array.from(obj, mapFn, thisArg) 创建单个数组。