Display line number in head and tail command like `cat -n`

Question

I'm trying to get the key of these json objects in order to create a new object with extra filed to create table headers in a React app. JSON data:

let example = [
  {
    id: 1,
    city: 'New York',
  },
 {
    id: 2,
    city: 'Paris',
  },
]

The function:

getKeys() {
    return example.map((key) => {
      return {
        cityName: key, // gets the whole array
        capital: false,
      };
    });
  }

I tries Object.keys( example);, it returns integers; 0, 1. How can I get the keys in this case? Thanks.

Solution

What about head and tail command? Is there any option to view the line number in head and tail without using cat -n and pipe the output to head or tail?

No; the current versions of head and tail do not have any way to add line numbers to the output themselves.

Comments

[Kusalananda]

-n is the option for selecting the number of lines that you'd want head or tail to return.

[Kusalananda]

There's nothing stopping the user from using head file | cat -n though.

[Jeff Schaller]

Yes, I was afraid I was being too brief; I was responding directly to the "can head or tail number lines directly?"