JavaScript flatMap() 错误：“flatMap 映射器 function 不可调用”

Question

I am trying to flatten an array with the following code, but when I use .flatMap() I get the error:

Uncaught TypeError: flatMap mapper function is not callable
    at Array.flatMap (<anonymous>)

const data = [
        { key1: 5, key3: 2 },
        { key1: 2, key3: 1 },
        { key1: 3, key3: 2 },
        { key2: 8 },
        { key1: 5, key3: 2 },
      ];
var allKeys = data.map(r => Object.keys(r))
// [
//   [ 'key1', 'key3' ],
//   [ 'key1', 'key3' ],
//   [ 'key1', 'key3' ],
//   [ 'key2' ],
//   [ 'key1', 'key3' ]
// ]
allKeys.flatMap();

Answer 1

In this case I should be using flat() not flatMap() . The below works as expected.

 const data = [ { key1: 5, key3: 2 }, { key1: 2, key3: 1 }, { key1: 3, key3: 2 }, { key2: 8 }, { key1: 5, key3: 2 }, ]; var allKeys = data.map(r => Object.keys(r)) console.log(allKeys.flat());

Answer 2

You could use flatMap instead of map to be more concise, which eliminates the need for calling .flat() after, as it is just shorthand for .map(...).flat() . As well, you can directly pass Object.keys as the callback for flatMap , as it ignores all arguments other than the first one that it is given.

 const data = [ { key1: 5, key3: 2 }, { key1: 2, key3: 1 }, { key1: 3, key3: 2 }, { key2: 8 }, { key1: 5, key3: 2 }, ]; var allKeys = data.flatMap(Object.keys) console.log(allKeys);