How to put jq output multi arrays in single array

While reading data from a json file using jq.
This command jq ".[]|keys" config.json gives following output:

[
  "N1",
  "N2"
]
[
  "N3",
  "N4"
]

What I ideally want is very simple:

["N1", "N2", "N3", "N4"]

However,
How I cannot find a way to accomplish this.

Config file:

{
    "Test1":{
        "N1":{
            "crn":"1",
            "con":"2"
        },
        "N2":{
            "crn":"100",
            "con":"200"
        }
        
    },
    "test2":{
        "N3":{
            "crn":"xx",
            "con":"2x"
        },
        "N4":{
            "crn":"xxxx",
            "con":"3xx"
        }
    }
}

>Solution :

Use map instead:

jq 'map(keys[])' config.json

[
  "N1",
  "N2",
  "N3",
  "N4"
]

Demo

Note that keys sorts the keys. If you want them unsorted, use keys_unsorted instead.

Also, if you want to have the output in one line, add the --compact-output (or -c) option (thx @Cyrus).