Cannot read then of undefined on promises

Question

I'm trying to get a response from a function, to execute another function, but I don't receive the response. I get the following error on: "TypeError: Cannot read property 'then' of undefined." I followed this tutorial, I tried to use Promises but no success. Here's my code

function i_emp() {
    const form = $("#msform");
    const formdata = getFormData(form); // Return a data inputs JSON
    const table_emp = formdata.table_emp;
    const json_emp = {
        // DATA HERE
    };
    $.ajax({
        url: "./class/Class_Insert.php",
        type: "POST",
        dataType: "json",
        data: {
            table_name: table_emp,
            data: json_emp,
        },
        success: function(result) {
            console.log(result);
        },
        error: function() {
            console.log({
                error: "Error"
            });
        }
    }).then(() => {
        return json_emp;
    });

    function env() {

        i_emp().then(function(result) {
            console.log(result);
        });

        // const resultado = i_emp();  // I tryed this one but no success
        // console.log(resultado); 

    }

Answer 1

function i_emp() {
  return new Promise(function(resolve, reject){
    const form = $("#msform");
    const formdata = getFormData(form); // Return a data inputs JSON
    const table_emp = formdata.table_emp;
    const json_emp = {
        // DATA HERE
    };
    $.ajax({
        url: "./class/Class_Insert.php",
        type: "POST",
        dataType: "json",
        data: {
            table_name: table_emp,
            data: json_emp,
        },
        success: function(result) {
            resolve(result);
        },
        error: function() {
            reject({
                error: "Error"
            });
        }
    });
 });
}

function env(){
 i_emp().then(function(result) {
  console.log(result);
 }, function(error){
  console.log(error);
 });
}