How to convert Ajax (Jquery) into fetch async

I wrote this code and it’s works perfect for me.
But when i try to convert it to fetch, dosen’t work because return a promise.
I don’t know how to use it as a async false on fetch.

            'getProjectConstants': function(constArray)
            {
                var result='';
                $.ajax({
                type:       "GET",
                url:        `${constProjectBaseUrl}/ajax/getProjectConstants/${constArray}`,
                async:      false,
                dataType:   "json",
                success: function(data) {
                result = data
            }
        });
        return result

I tried to do like this, but dosen’t work

        fetch(`${constProjectBaseUrl}/ajax/getProjectConstants/${constArray}`)
        .then((response) => response.json())
        .then((response) => {
             // console.log(response)
             return response
        }) // end of .then((response) => {
        .catch(error => {
             console.log("[ajax.getProjectConstants] Error => " + error);
        }); // end of .catch(error => {