diff --git a/htdocs/js/loris-scripts.js b/htdocs/js/loris-scripts.js
index d07ae39f48..f49b6e74f9 100644
--- a/htdocs/js/loris-scripts.js
+++ b/htdocs/js/loris-scripts.js
@@ -1,5 +1,70 @@
 /* eslint new-cap: ["error", {capIsNewExceptions: ["DynamicTable", "FileUpload"]}]*/
 
+/**
+ * Display the login modal when a request returns a 401 response.
+ */
+function handleUnauthorized() {
+  if (!window.$ || !window.loris) {
+    return;
+  }
+
+  if (!$('#login-modal').length) {
+    return;
+  }
+
+  if ($('#login-modal').hasClass('in')) {
+    $('#login-modal-error').show();
+    return;
+  }
+
+  $('#login-modal').modal('show');
+  $('#modal-login')
+    .off('click.lorisFetch')
+    .on('click.lorisFetch', function(e) {
+      e.preventDefault();
+      let data = {
+        username: $('#modal-username').val(),
+        password: $('#modal-password').val(),
+        login: 'Login',
+      };
+
+      window.lorisFetch(window.loris.BaseURL, {
+        method: 'POST',
+        headers: {
+          'Content-Type': 'application/x-www-form-urlencoded; charset=UTF-8',
+        },
+        body: new URLSearchParams(data),
+      })
+        .then((response) => {
+          if (!response.ok) {
+            throw new Error('request_failed');
+          }
+          $('#login-modal-error').hide();
+          $('#login-modal').modal('hide');
+        })
+        .catch(() => {
+          $('#login-modal-error').show();
+        });
+    });
+}
+
+if (!window.lorisFetch) {
+  window.lorisFetch = function(input, init) {
+    const options = Object.assign(
+      {
+        credentials: 'same-origin',
+      },
+      init || {}
+    );
+    return fetch(input, options).then((response) => {
+      if (response.status === 401) {
+        handleUnauthorized();
+      }
+      return response;
+    });
+  };
+}
+
 $(document).ready(function() {
   $('#menu-toggle').click(function(e) {
     e.preventDefault();
@@ -8,30 +73,3 @@ $(document).ready(function() {
   $('.dynamictable').DynamicTable();
   $('.fileUpload').FileUpload();
 });
-
-$(document).ajaxError(function(event, jqxhr, settings, thrownError) {
-  if (jqxhr.status === 401) {
-    if ($('#login-modal').hasClass('in')) {
-      $('#login-modal-error').show();
-    } else {
-      $('#login-modal').modal('show');
-      $('#modal-login').click(function(e) {
-        e.preventDefault();
-        let data = {
-          username: $('#modal-username').val(),
-          password: $('#modal-password').val(),
-          login: 'Login',
-        };
-        $.ajax({
-          type: 'post',
-          url: loris.BaseURL,
-          data: data,
-          success: function() {
-            $('#login-modal-error').hide();
-            $('#login-modal').modal('hide');
-          },
-        });
-      });
-    }
-  }
-});
diff --git a/jslib/lorisFetch.js b/jslib/lorisFetch.js
new file mode 100644
index 0000000000..1aba03792c
--- /dev/null
+++ b/jslib/lorisFetch.js
@@ -0,0 +1,81 @@
+/**
+ * Display the login modal when a request returns a 401 response.
+ */
+function handleUnauthorized() {
+  if (typeof window === 'undefined') {
+    return;
+  }
+  if (!window.$ || !window.loris) {
+    return;
+  }
+
+  const $ = window.$;
+  if (!$('#login-modal').length) {
+    return;
+  }
+
+  if ($('#login-modal').hasClass('in')) {
+    $('#login-modal-error').show();
+    return;
+  }
+
+  $('#login-modal').modal('show');
+  $('#modal-login')
+    .off('click.lorisFetch')
+    .on('click.lorisFetch', function(e) {
+      e.preventDefault();
+      let data = {
+        username: $('#modal-username').val(),
+        password: $('#modal-password').val(),
+        login: 'Login',
+      };
+
+      fetch(window.loris.BaseURL, {
+        method: 'POST',
+        headers: {
+          'Content-Type': 'application/x-www-form-urlencoded; charset=UTF-8',
+        },
+        body: new URLSearchParams(data),
+        credentials: 'same-origin',
+      })
+        .then((response) => {
+          if (!response.ok) {
+            throw new Error('request_failed');
+          }
+          $('#login-modal-error').hide();
+          $('#login-modal').modal('hide');
+        })
+        .catch(() => {
+          $('#login-modal-error').show();
+        });
+    });
+}
+
+/**
+ * Wrapper around fetch that keeps credentials and handles 401s.
+ *
+ * @param {*} input
+ * @param {object=} init
+ * @return {Promise<Response>}
+ */
+function lorisFetch(input, init) {
+  const options = Object.assign(
+    {
+      credentials: 'same-origin',
+    },
+    init || {}
+  );
+
+  return fetch(input, options).then((response) => {
+    if (response.status === 401) {
+      handleUnauthorized();
+    }
+    return response;
+  });
+}
+
+if (typeof window !== 'undefined') {
+  window.lorisFetch = lorisFetch;
+}
+
+export default lorisFetch;
diff --git a/modules/configuration/js/cohort.js b/modules/configuration/js/cohort.js
index aa7070bf74..fc0a8ff803 100644
--- a/modules/configuration/js/cohort.js
+++ b/modules/configuration/js/cohort.js
@@ -1,5 +1,6 @@
 $(document).ready(function() {
     "use strict";
+    var lorisFetch = window.lorisFetch || fetch;
     $('div').tooltip();
     $(".savecohort").click(function(e) {
         var form = $(e.currentTarget).closest('form');
@@ -11,48 +12,58 @@ $(document).ready(function() {
         var recruitmentTarget = $(form.find(".cohortRecruitmentTarget")).val();
         e.preventDefault();
 
-        $.ajax(
-                {
-                    "type" : "post",
-                    "url" : loris.BaseURL + "/configuration/ajax/updateCohort.php",
-                    "data" : {
+        lorisFetch(loris.BaseURL + "/configuration/ajax/updateCohort.php", {
+                    method: "post",
+                    headers: {
+                      "Content-Type": "application/x-www-form-urlencoded; charset=UTF-8",
+                    },
+                    body: new URLSearchParams({
                         "cohortID" : cohortID,
                         "title" : title,
                         "useEDC" : useEDC,
                         "WindowDifference" : windowDifference,
                         "RecruitmentTarget" : recruitmentTarget,
-                    },
-                    "dataType": "json",
-                    "success" : function(data) {
-                        $(form.find(".saveStatus"))
-                        .text(data.ok)
-                        .css({ 'color': 'green'})
-                        .fadeIn(500)
-                        .delay(1000);
-                      if (cohortID === 'new') {
-                        setTimeout(function(){
-                          location.reload();
-                        }, 1000);
-                      } else {
-                        var projectDiv = document.getElementById(`#cohort${cohortID}`);
-                        var Name = projectDiv.innerText;
-                        projectDiv.innerText = title;
-                        var projectHeader = document.getElementById(`cohort${cohortID}`);
-                        projectHeader.children[0].innerText = title + projectHeader.children[0].innerText.substring(
-                          Name.length
-                        );
-                      }
-                    },
-                    "error" : function(data) {
-                        $(form.find(".saveStatus"))
-                        .text(data.responseJSON.error)
-                        .css({ 'color': 'red'})
-                        .fadeIn(500)
-                        .delay(1000);
+                    }),
+                    credentials: "same-origin",
+                })
+                .then(async function(response) {
+                    var text = await response.text();
+                    var data = null;
+                    try {
+                      data = JSON.parse(text);
+                    } catch (err) {
+                      data = null;
                     }
-                }
-
-          );
+                    if (!response.ok) {
+                      throw {error: (data && data.error) ? data.error : text};
+                    }
+                    $(form.find(".saveStatus"))
+                    .text(data && data.ok ? data.ok : "Saved")
+                    .css({ 'color': 'green'})
+                    .fadeIn(500)
+                    .delay(1000);
+                  if (cohortID === 'new') {
+                    setTimeout(function(){
+                      location.reload();
+                    }, 1000);
+                  } else {
+                    var projectDiv = document.getElementById(`#cohort${cohortID}`);
+                    var Name = projectDiv.innerText;
+                    projectDiv.innerText = title;
+                    var projectHeader = document.getElementById(`cohort${cohortID}`);
+                    projectHeader.children[0].innerText = title + projectHeader.children[0].innerText.substring(
+                      Name.length
+                    );
+                  }
+                })
+                .catch(function(data) {
+                    var message = data && data.error ? data.error : 'Request failed.';
+                    $(form.find(".saveStatus"))
+                    .text(message)
+                    .css({ 'color': 'red'})
+                    .fadeIn(500)
+                    .delay(1000);
+                });
 
 
     });
diff --git a/modules/configuration/jsx/configuration_helper.js b/modules/configuration/jsx/configuration_helper.js
index 010d406bea..144523badc 100644
--- a/modules/configuration/jsx/configuration_helper.js
+++ b/modules/configuration/jsx/configuration_helper.js
@@ -1,4 +1,5 @@
 import swal from 'sweetalert2';
+import lorisFetch from 'jslib/lorisFetch';
 
 $(function() {
   'use strict';
@@ -59,11 +60,17 @@ $(function() {
         let id = $(this).attr('name');
         let button = this;
 
-        $.ajax({
-          type: 'post',
-          url: loris.BaseURL + '/configuration/ajax/process.php',
-          data: {remove: id},
-          success: function() {
+        lorisFetch(loris.BaseURL + '/configuration/ajax/process.php', {
+          method: 'post',
+          headers: {
+            'Content-Type': 'application/x-www-form-urlencoded; charset=UTF-8',
+          },
+          body: new URLSearchParams({remove: id}),
+        })
+          .then((response) => {
+            if (!response.ok) {
+              throw new Error('request_failed');
+            }
             if ($(button)
               .parent().parent().parent().children()
               .length > 1
@@ -83,12 +90,10 @@ $(function() {
                 .addClass('remove-new')
                 .removeClass('btn-remove');
             }
-          },
-          error: function(xhr, desc, err) {
-            console.error(xhr);
-            console.error('Details: ' + desc + '\nError:' + err);
-          },
-        });
+          })
+          .catch((err) => {
+            console.error(err);
+          });
       }
     });
   });
@@ -102,23 +107,31 @@ $(function() {
     // Clear previous feedback
     $('.submit-area > label').remove();
 
-    $.ajax({
-      type: 'post',
-      url: loris.BaseURL + '/configuration/ajax/process.php',
-      data: form,
-      success: function() {
+    lorisFetch(loris.BaseURL + '/configuration/ajax/process.php', {
+      method: 'post',
+      headers: {
+        'Content-Type': 'application/x-www-form-urlencoded; charset=UTF-8',
+      },
+      body: form,
+    })
+      .then(async (response) => {
+        if (!response.ok) {
+          let text = await response.text();
+          let error = new Error('request_failed');
+          error.lorisMessage = text;
+          throw error;
+        }
         let html = '<label>Submitted</label>';
         $(html)
           .hide()
           .appendTo('.submit-area')
           .fadeIn(500).delay(1000).fadeOut(500);
         location.reload();
-      },
-      error: function(xhr, desc, err) {
-        let html = '<label>' + xhr.responseText + '</label>';
+      })
+      .catch((error) => {
+        let html = '<label>' + (error.lorisMessage || '') + '</label>';
         $(html).hide().appendTo('.submit-area').fadeIn(500).delay(1000);
-      },
-    });
+      });
   });
 
   // On form reset, to delete the elements added with the "Add field" button that were not submitted.