Call function with request options from another function always empty

Question

I have a code like below. I am running a calling a function searchApiData. In searchApiData, when I log data in console I can see values of body. But when I see from exports.readData console.log(returnData), the value is always empty. Anyone know how I can get the data of the body in searchApiData?

exports.readData = functions.https.onRequest(async (req, res) => {
 var returnData = "";
 for (var a = 0; a < emailList.length; a++) {
    returnData = searchApiData(emailList[a]);
    console.log(returnData);
 } 
})

function searchApiData(email) {
    fsData = "";
    const options = {
        method: 'GET',
        json: true,
        url: FS_URL + 'api/lookup?f=email&q='+email+'&entities=contact',
        headers: {
            "Authorization": "Token token=" + FS_API_KEY,
            "Content-Type": "application/json"
        }
    };
    
    //call the request
    request(options, function(error, response, body) {
      if(!error && response.statusCode == 200){
        console.log(body);
         fsData = body;
      } else{
        console.log(error);
      }
    });
    return fsData;
}