Extract value from array of objects in Postman

If it is an array of objects, then just select the first object using index [0] before grabbing the object's key like this:

var data = JSON.parse(responseBody);   
postman.setEnvironmentVariable("userid", data[0].Id);

This works like charm! Basically what i am doing here is, parse the response and from the data array, take id and save it in postman environment variable.

var jsonData = JSON.parse(responseBody);
    for (var i = 0; i < jsonData.data.length; i++) `
    {
    var counter = jsonData.data[i];
    postman.setEnvironmentVariable("schID", counter.id);
    }