What does "Array.from() does not create an intermediate array" mean?

Question

From MDN Web Docs, Array.from(obj, mapFn, thisArg) has the same result as Array.from(obj).map(mapFn, thisArg), except that it does not create an intermediate array.

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.

What does "Array.from() does not create an intermediate array" mean?

Kaiido · Accepted Answer · 2020-03-28 10:07:05Z

2

You can decompose Array.from(obj).map(mapFn, thisArg) to

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

Two Arrays have been created since both Array.from() and Array.prototype.map do return a new Array.

Array.from(obj, mapFn, thisArg) creates a single Array.

answered Mar 28, 2020 at 10:07

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Kaiido

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