diff --git a/umap/static/umap/js/modules/request.js b/umap/static/umap/js/modules/request.js
index a3aaf158..54347394 100644
--- a/umap/static/umap/js/modules/request.js
+++ b/umap/static/umap/js/modules/request.js
@@ -17,15 +17,15 @@ const BaseRequest = Evented.extend({
     } catch (error) {
       this._onError(error)
       this.fire('dataload', { id: id })
-      return
+      return null
     }
     if (!response.ok) {
-      this.onNok(response.status, await response.text())
+      this.fire('dataload', { id: id })
+      return this.onNok(response.status, response)
     }
     // TODO
     // - error handling
     // - UI connection / events
-    // - preflight mode in CORS ?
 
     this.fire('dataload', { id: id })
     return response
@@ -44,7 +44,9 @@ const BaseRequest = Evented.extend({
     this.onError(error)
   },
   onError: function (error) {},
-  onNok: function (status) {},
+  onNok: function (status, reponse) {
+    return response
+  },
 })
 
 export const Request = BaseRequest.extend({
@@ -55,8 +57,9 @@ export const Request = BaseRequest.extend({
     console.error(error)
     this.ui.alert({ content: L._('Problem in the response'), level: 'error' })
   },
-  onNok: function (status, message) {
+  onNok: function (status, response) {
     this.onError(message)
+    return response
   },
 })
 
@@ -81,26 +84,30 @@ export const ServerRequest = Request.extend({
       headers['X-CSRFToken'] = token
     }
     const response = await Request.prototype.post.call(this, uri, headers, data)
-    return await this._handle_json_response(response)
+    return await this._as_json(response)
   },
 
   get: async function (uri, headers) {
     const response = await Request.prototype.get.call(this, uri, headers)
-    return await this._handle_json_response(response)
+    return await this._as_json(response)
   },
 
-  _handle_json_response: async function (response) {
+  _as_json: async function (response) {
+    if (!response) return [{}, null, new Error("Undefined error")]
     try {
       const data = await response.json()
-      this._handle_server_instructions(data)
-      return [data, response]
+      if (this._handle_server_instructions(data) !== false) {
+        return [{}, null]
+      }
+      return [data, response, null]
     } catch (error) {
       this._onError(error)
+      return [{}, null, error]
     }
   },
 
   _handle_server_instructions: function (data) {
-    // In some case, the response contains instructions
+    // Generic cases, let's deal with them once
     if (data.redirect) {
       const newPath = data.redirect
       if (window.location.pathname == newPath) {
@@ -122,6 +129,9 @@ export const ServerRequest = Request.extend({
         this.fire('login')
         win.close()
       }
+    } else {
+      // Nothing to do, we can let the response proceed
+      return false
     }
   },
 
diff --git a/umap/static/umap/js/umap.datalayer.permissions.js b/umap/static/umap/js/umap.datalayer.permissions.js
index f4a79e92..8ac2a2d7 100644
--- a/umap/static/umap/js/umap.datalayer.permissions.js
+++ b/umap/static/umap/js/umap.datalayer.permissions.js
@@ -55,10 +55,16 @@ L.U.DataLayerPermissions = L.Class.extend({
     if (!this.isDirty) return this.datalayer.map.continueSaving()
     const formData = new FormData()
     formData.append('edit_status', this.options.edit_status)
-    await this.datalayer.map.server.post(this.getUrl(), {}, formData)
-    this.commit()
-    this.isDirty = false
-    this.datalayer.map.continueSaving()
+    const [data, response, error] = await this.datalayer.map.server.post(
+      this.getUrl(),
+      {},
+      formData
+    )
+    if (!error) {
+      this.commit()
+      this.isDirty = false
+      this.datalayer.map.continueSaving()
+    }
   },
 
   commit: function () {
diff --git a/umap/static/umap/js/umap.forms.js b/umap/static/umap/js/umap.forms.js
index 3f36b184..f2776ae8 100644
--- a/umap/static/umap/js/umap.forms.js
+++ b/umap/static/umap/js/umap.forms.js
@@ -695,11 +695,13 @@ L.FormBuilder.IconUrl = L.FormBuilder.BlurInput.extend({
     if (this.pictogram_list) {
       this.buildSymbolsList()
     } else {
-      const [{ pictogram_list }, response] = await this.builder.map.server.get(
+      const [{ pictogram_list }, response, error] = await this.builder.map.server.get(
         this.builder.map.options.urls.pictogram_list_json
       )
-      this.pictogram_list = pictogram_list
-      this.buildSymbolsList()
+      if (!error) {
+        this.pictogram_list = pictogram_list
+        this.buildSymbolsList()
+      }
     }
   },
 
diff --git a/umap/static/umap/js/umap.js b/umap/static/umap/js/umap.js
index f142f249..f5ce6c88 100644
--- a/umap/static/umap/js/umap.js
+++ b/umap/static/umap/js/umap.js
@@ -34,7 +34,7 @@ L.Map.mergeOptions({
   // we cannot rely on this because of the y is overriden by Leaflet
   // See https://github.com/Leaflet/Leaflet/pull/9201
   // And let's remove this -y when this PR is merged and released.
-  demoTileInfos: { s: 'a', z: 9, x: 265, y: 181, '-y': 181, r: '' },
+  demoTileInfos: { 's': 'a', 'z': 9, 'x': 265, 'y': 181, '-y': 181, 'r': '' },
   licences: [],
   licence: '',
   enableMarkerDraw: true,
@@ -838,7 +838,10 @@ L.U.Map.include({
         self.isDirty = true
       }
     if (this._controls.tilelayersChooser)
-      this._controls.tilelayersChooser.openSwitcher({ callback: callback, className: 'dark' })
+      this._controls.tilelayersChooser.openSwitcher({
+        callback: callback,
+        className: 'dark',
+      })
   },
 
   manageDatalayers: function () {
@@ -1097,59 +1100,61 @@ L.U.Map.include({
     formData.append('center', JSON.stringify(this.geometry()))
     formData.append('settings', JSON.stringify(geojson))
     const uri = this.urls.get('map_save', { map_id: this.options.umap_id })
-    const [data, response] = await this.server.post(uri, {}, formData)
-    let duration = 3000,
-      alert = { content: L._('Map has been saved!'), level: 'info' }
-    if (!this.options.umap_id) {
-      alert.content = L._('Congratulations, your map has been created!')
-      this.options.umap_id = data.id
-      this.permissions.setOptions(data.permissions)
-      this.permissions.commit()
-      if (
-        data.permissions &&
-        data.permissions.anonymous_edit_url &&
-        this.options.urls.map_send_edit_link
-      ) {
-        alert.duration = Infinity
-        alert.content =
-          L._(
-            'Your map has been created! As you are not logged in, here is your secret link to edit the map, please keep it safe:'
-          ) + `<br>${data.permissions.anonymous_edit_url}`
+    const [data, response, error] = await this.server.post(uri, {}, formData)
+    if (!error) {
+      let duration = 3000,
+        alert = { content: L._('Map has been saved!'), level: 'info' }
+      if (!this.options.umap_id) {
+        alert.content = L._('Congratulations, your map has been created!')
+        this.options.umap_id = data.id
+        this.permissions.setOptions(data.permissions)
+        this.permissions.commit()
+        if (
+          data.permissions &&
+          data.permissions.anonymous_edit_url &&
+          this.options.urls.map_send_edit_link
+        ) {
+          alert.duration = Infinity
+          alert.content =
+            L._(
+              'Your map has been created! As you are not logged in, here is your secret link to edit the map, please keep it safe:'
+            ) + `<br>${data.permissions.anonymous_edit_url}`
 
-        alert.actions = [
-          {
-            label: L._('Send me the link'),
-            input: L._('Email'),
-            callback: this.sendEditLink,
-            callbackContext: this,
-          },
-          {
-            label: L._('Copy link'),
-            callback: () => {
-              L.Util.copyToClipboard(data.permissions.anonymous_edit_url)
-              this.ui.alert({
-                content: L._('Secret edit link copied to clipboard!'),
-                level: 'info',
-              })
+          alert.actions = [
+            {
+              label: L._('Send me the link'),
+              input: L._('Email'),
+              callback: this.sendEditLink,
+              callbackContext: this,
             },
-            callbackContext: this,
-          },
-        ]
+            {
+              label: L._('Copy link'),
+              callback: () => {
+                L.Util.copyToClipboard(data.permissions.anonymous_edit_url)
+                this.ui.alert({
+                  content: L._('Secret edit link copied to clipboard!'),
+                  level: 'info',
+                })
+              },
+              callbackContext: this,
+            },
+          ]
+        }
+      } else if (!this.permissions.isDirty) {
+        // Do not override local changes to permissions,
+        // but update in case some other editors changed them in the meantime.
+        this.permissions.setOptions(data.permissions)
+        this.permissions.commit()
       }
-    } else if (!this.permissions.isDirty) {
-      // Do not override local changes to permissions,
-      // but update in case some other editors changed them in the meantime.
-      this.permissions.setOptions(data.permissions)
-      this.permissions.commit()
+      // Update URL in case the name has changed.
+      if (history && history.pushState)
+        history.pushState({}, this.options.name, data.url)
+      else window.location = data.url
+      alert.content = data.info || alert.content
+      this.once('saved', () => this.ui.alert(alert))
+      this.ui.closePanel()
+      this.permissions.save()
     }
-    // Update URL in case the name has changed.
-    if (history && history.pushState)
-      history.pushState({}, this.options.name, data.url)
-    else window.location = data.url
-    alert.content = data.info || alert.content
-    this.once('saved', () => this.ui.alert(alert))
-    this.ui.closePanel()
-    this.permissions.save()
   },
 
   save: function () {
diff --git a/umap/static/umap/js/umap.layer.js b/umap/static/umap/js/umap.layer.js
index bdae1f3a..cbb17f20 100644
--- a/umap/static/umap/js/umap.layer.js
+++ b/umap/static/umap/js/umap.layer.js
@@ -674,22 +674,24 @@ L.U.DataLayer = L.Evented.extend({
     if (!this.umap_id) return
     if (this._loading) return
     this._loading = true
-    const [geojson, response] = await this.map.server.get(this._dataUrl())
-    this._last_modified = response.headers['Last-Modified']
-    // FIXME: for now this property is set dynamically from backend
-    // And thus it's not in the geojson file in the server
-    // So do not let all options to be reset
-    // Fix is a proper migration so all datalayers settings are
-    // in DB, and we remove it from geojson flat files.
-    if (geojson._umap_options) {
-      geojson._umap_options.editMode = this.options.editMode
+    const [geojson, response, error] = await this.map.server.get(this._dataUrl())
+    if (!error) {
+      this._last_modified = response.headers['Last-Modified']
+      // FIXME: for now this property is set dynamically from backend
+      // And thus it's not in the geojson file in the server
+      // So do not let all options to be reset
+      // Fix is a proper migration so all datalayers settings are
+      // in DB, and we remove it from geojson flat files.
+      if (geojson._umap_options) {
+        geojson._umap_options.editMode = this.options.editMode
+      }
+      // In case of maps pre 1.0 still around
+      if (geojson._storage) geojson._storage.editMode = this.options.editMode
+      this.fromUmapGeoJSON(geojson)
+      this.backupOptions()
+      this.fire('loaded')
+      this._loading = false
     }
-    // In case of maps pre 1.0 still around
-    if (geojson._storage) geojson._storage.editMode = this.options.editMode
-    this.fromUmapGeoJSON(geojson)
-    this.backupOptions()
-    this.fire('loaded')
-    this._loading = false
   },
 
   fromGeoJSON: function (geojson) {
@@ -749,8 +751,10 @@ L.U.DataLayer = L.Evented.extend({
       url = this.map.proxyUrl(url, this.options.remoteData.ttl)
     const response = await this.map.request.get(url)
     this.clear()
-    this.rawToGeoJSON(await response.text(), this.options.remoteData.format, (geojson) =>
-      this.fromGeoJSON(geojson)
+    this.rawToGeoJSON(
+      await response.text(),
+      this.options.remoteData.format,
+      (geojson) => this.fromGeoJSON(geojson)
     )
   },
 
@@ -1391,8 +1395,10 @@ L.U.DataLayer = L.Evented.extend({
 
     const versionsContainer = L.DomUtil.createFieldset(container, L._('Versions'), {
       callback: async function () {
-        const [{versions}, response] = await this.map.server.get(this.getVersionsUrl())
-        versions.forEach(appendVersion)
+        const [{ versions }, response, error] = await this.map.server.get(
+          this.getVersionsUrl()
+        )
+        if (!error) versions.forEach(appendVersion)
       },
       context: this,
     })
@@ -1401,13 +1407,17 @@ L.U.DataLayer = L.Evented.extend({
   restore: async function (version) {
     if (!this.map.editEnabled) return
     if (!confirm(L._('Are you sure you want to restore this version?'))) return
-    const [geojson, response] = await this.map.server.get(this.getVersionUrl(version))
-    if (geojson._storage) geojson._umap_options = geojson._storage // Retrocompat.
-    if (geojson._umap_options) this.setOptions(geojson._umap_options)
-    this.empty()
-    if (this.isRemoteLayer()) this.fetchRemoteData()
-    else this.addData(geojson)
-    this.isDirty = true
+    const [geojson, response, error] = await this.map.server.get(
+      this.getVersionUrl(version)
+    )
+    if (!error) {
+      if (geojson._storage) geojson._umap_options = geojson._storage // Retrocompat.
+      if (geojson._umap_options) this.setOptions(geojson._umap_options)
+      this.empty()
+      if (this.isRemoteLayer()) this.fetchRemoteData()
+      else this.addData(geojson)
+      this.isDirty = true
+    }
   },
 
   featuresToGeoJSON: function () {
@@ -1544,27 +1554,33 @@ L.U.DataLayer = L.Evented.extend({
       map_id: this.map.options.umap_id,
       pk: this.umap_id,
     })
-    const headers =  this._last_modified
+    const headers = this._last_modified
       ? { 'If-Unmodified-Since': this._last_modified }
       : {}
-    const [data, response] = await this.map.server.post(saveUrl, headers, formData)
-    // Response contains geojson only if save has conflicted and conflicts have
-    // been resolved. So we need to reload to get extra data (saved from someone else)
-    if (data.geojson) {
-      this.clear()
-      this.fromGeoJSON(data.geojson)
-      delete data.geojson
+    const [data, response, error] = await this.map.server.post(
+      saveUrl,
+      headers,
+      formData
+    )
+    if (!error) {
+      // Response contains geojson only if save has conflicted and conflicts have
+      // been resolved. So we need to reload to get extra data (saved from someone else)
+      if (data.geojson) {
+        this.clear()
+        this.fromGeoJSON(data.geojson)
+        delete data.geojson
+      }
+      this._geojson = geojson
+      this._last_modified = response.headers['Last-Modified']
+      this.setUmapId(data.id)
+      this.updateOptions(data)
+      this.backupOptions()
+      this.connectToMap()
+      this._loaded = true
+      this.redraw() // Needed for reordering features
+      this.isDirty = false
+      this.permissions.save()
     }
-    this._geojson = geojson
-    this._last_modified = response.headers['Last-Modified']
-    this.setUmapId(data.id)
-    this.updateOptions(data)
-    this.backupOptions()
-    this.connectToMap()
-    this._loaded = true
-    this.redraw() // Needed for reordering features
-    this.isDirty = false
-    this.permissions.save()
   },
 
   saveDelete: async function () {
diff --git a/umap/static/umap/js/umap.permissions.js b/umap/static/umap/js/umap.permissions.js
index 087f0c0c..de5544fe 100644
--- a/umap/static/umap/js/umap.permissions.js
+++ b/umap/static/umap/js/umap.permissions.js
@@ -132,13 +132,15 @@ L.U.MapPermissions = L.Class.extend({
   },
 
   attach: async function () {
-    await this.map.server.post(this.getAttachUrl())
-    this.options.owner = this.map.options.user
-    this.map.ui.alert({
-      content: L._('Map has been attached to your account'),
-      level: 'info',
-    })
-    this.map.ui.closePanel()
+    const [data, response, error] = await this.map.server.post(this.getAttachUrl())
+    if (!error) {
+      this.options.owner = this.map.options.user
+      this.map.ui.alert({
+        content: L._('Map has been attached to your account'),
+        level: 'info',
+      })
+      this.map.ui.closePanel()
+    }
   },
 
   save: async function () {
@@ -155,11 +157,17 @@ L.U.MapPermissions = L.Class.extend({
       formData.append('owner', this.options.owner && this.options.owner.id)
       formData.append('share_status', this.options.share_status)
     }
-    await this.map.server.post(this.getUrl(), {}, formData)
-    this.commit()
-    this.isDirty = false
-    this.map.continueSaving()
-    this.map.fire('postsync')
+    const [data, response, error] = await this.map.server.post(
+      this.getUrl(),
+      {},
+      formData
+    )
+    if (!error) {
+      this.commit()
+      this.isDirty = false
+      this.map.continueSaving()
+      this.map.fire('postsync')
+    }
   },
 
   getUrl: function () {