Javascript - 数组上的 flatMap 方法 - （flatMap 不是函数）

Question

According to the Mozilla Developer Website:

The flatMap() method first maps each element using a mapping function, then flattens the result into a new array. It is identical to a map followed by a flat of depth 1, but flatMap is often quite useful, as merging both into one method is slightly more efficient.

Example:

let arr = [1, 2, 4, 2, 3, 3, 4, 5, 5, 5, 8, 8, 9, 10];

const flatMap = arr.flatMap(x => x);
console.log(flatMap);

TypeError: arr.flatMap() is not a function

Why is this returning this error?

EDIT

I am running this through Atom text editor and have used HomeBrew to update it to the latest version using brew upgrade node and it is still giving me the same error.

I have also tried npm install n -g

Answer 1

I was getting this when testing with jest, it's because flatmap is only part of node 11 and I was using node 10.

As a workaround, I added require('core-js/stable'); in my setupTests.ts .

I presume also there are some browsers that won't have this either. As such I will also put that require line in my application imports somewhere.

Answer 2

It seems that flatMap is not supported on your browser. Here you are a complete list of supported browsers: https://caniuse.com/#search=flatMap

If you really want to use it, here you are a polyfill that will grant support down to ES3: https://www.npmjs.com/package/array.prototype.flatmap

By the way, it is useful when applied on a multidimensional array!

Answer 3

It means you're using a web browser or other development environment that does not support Array.prototype.flatMap (currently Edge and IE have no support). CanIUse table here .

Also note that it is used primarily for multidimensional arrays (to avoid chaining map and flat , hence flatMap ).