GetExternalUsers.js

(function() {
    var allResults = [],
        queryText = encodeURIComponent("#ext# contentclass:spspeople"),
        rowLimit = 500,
        selectProperties = ["AccountName", "PreferredName", "WorkEmail"];

    function chunk (arr, len) {
      var chunks = [],
          i = 0,
          n = arr.length;

      while (i < n) {
        chunks.push(arr.slice(i, i += len));
      }

      return chunks;
    }

    function mapResult(value) {
        var obj = {};
        value.Cells.results.forEach(function(item) {
           if(selectProperties.indexOf(item.Key) > -1) {
               obj[item.Key] = item.Value;
           }
        });
        return obj;
    }

    function getResults(startRow) {
        if(!startRow)
            startRow = 0;

        var queryUrl = _spPageContextInfo.webAbsoluteUrl + "/_api/search/query?querytext='" + queryText + "'&rowlimit=" + rowLimit + "&startrow=" + startRow + "&trimduplicates=false&selectproperties='" + selectProperties.join(",") + "'&sourceid='b09a7990-05ea-4af9-81ef-edfab16c4e31'";

        return jQuery.ajax({
            url: queryUrl,
            async: true,
            method: "GET",
            headers: {
                "Accept": "application/json; odata=verbose"
            }
        })
        .then(function (data) {            
            var totalRowCount = data.d.query.PrimaryQueryResult.RelevantResults.TotalRows,
                results = data.d.query.PrimaryQueryResult.RelevantResults.Table.Rows.results,
                resultsMapped = jQuery.map(results, mapResult);

            allResults = resultsMapped.concat(allResults); // add sites to allSites array
            // if there are more results ? get the next page : return the results
            return startRow + rowLimit < totalRowCount ? getResults(startRow + rowLimit) : allResults.sort(function(a, b) { return a[selectProperties[0]].localeCompare(b[selectProperties[0]]); });
        });
    }

    getResults().then(function(results) {
        var chunks = chunk(results, 1000); // split results into 1000 row chunks (limit for Chrome console.table)
        chunks.forEach(function(chunk) {
            console.table(chunk);
        });
    });
})();