find the length of array using map function ES6

Question

I'm trying to find the length of an array using ES6 using the below code but it does not work.

a=[[1,2,3,4],[4,5,6]]
result = a.map(d=>({d[0]:d.length}))
console.log(result)

This works:-

a=[[1,2,3,4],[4,5,6]]
result = a.map(d=>({name:d[0], length:d.length}))
console.log(result)

are you asking why the first doesn't work but the second one does? — Nick Parsons, Dec 21 '19 at 00:03
Because the first is invalid syntax, and your engine should tell you that with an error message. I'll search a dupe target on how to use computed property names... — ASDFGerte, Dec 21 '19 at 00:04

score 0 · Answer 1 · answered Dec 21 '19 at 00:05

I think you're looking for something like this if you're trying to end up with an array of objects with the first element of the original array as the property name and the length of the array as the property value:

a=[[1,2,3,4],[4,5,6]]
result = a.map(d=>({[d[0]]:d.length}))
console.log(result)

score 0 · Accepted Answer · answered Dec 21 '19 at 00:17

Using ES6, to create a key for an object from a variable, you have to wrap with [].

For example:

const a = 'first name';
const name = {
  [a]: 'john',
};

console.log(name);

So this is what you are looking for:

a=[[1,2,3,4],[4,5,6]]
result = a.map(d=>({[d[0]]:d.length}))
console.log(result)

find the length of array using map function ES6

2 Answers2