diff --git a/changelog/unreleased/enhancement-replace-deprecated-substr b/changelog/unreleased/enhancement-replace-deprecated-substr
new file mode 100644
index 00000000000..67a336ebe1e
--- /dev/null
+++ b/changelog/unreleased/enhancement-replace-deprecated-substr
@@ -0,0 +1,7 @@
+Enhancement: Replace deprecated String.prototype.substr()
+
+We've replaced all occurrences of the deprecated String.prototype.substr()
+function with String.prototype.slice() which works similarly but isn't
+deprecated.
+
+https://github.com/owncloud/web/pull/6718
diff --git a/packages/web-app-files/src/mixins/actions/rename.js b/packages/web-app-files/src/mixins/actions/rename.js
index 7e42d397171..3ef3395758b 100644
--- a/packages/web-app-files/src/mixins/actions/rename.js
+++ b/packages/web-app-files/src/mixins/actions/rename.js
@@ -165,7 +165,7 @@ export default {
           this.hideModal()
 
           if (sameResource) {
-            const newPath = resource.path.substr(1, resource.path.lastIndexOf('/'))
+            const newPath = resource.path.slice(1, resource.path.lastIndexOf('/') + 1)
             this.$router.push({
               params: {
                 item: '/' + newPath + newName || '/'
diff --git a/packages/web-app-files/src/mixins/deleteResources.js b/packages/web-app-files/src/mixins/deleteResources.js
index b0c3cbada39..4b9ed43af4b 100644
--- a/packages/web-app-files/src/mixins/deleteResources.js
+++ b/packages/web-app-files/src/mixins/deleteResources.js
@@ -170,7 +170,8 @@ export default {
           isSameResource(this.resourcesToDelete[0], this.currentFolder)
         ) {
           const resourcePath = this.resourcesToDelete[0].path
-          parentFolderPath = resourcePath.substr(0, resourcePath.lastIndexOf('/'))
+          const lastSlash = resourcePath.lastIndexOf('/')
+          parentFolderPath = resourcePath.slice(0, lastSlash !== -1 ? lastSlash : 0)
         }
 
         if (parentFolderPath !== undefined) {
diff --git a/packages/web-app-files/src/store/actions.js b/packages/web-app-files/src/store/actions.js
index e872d199f23..1e03c9a885a 100644
--- a/packages/web-app-files/src/store/actions.js
+++ b/packages/web-app-files/src/store/actions.js
@@ -128,7 +128,7 @@ export default {
   },
   renameFile(context, { file, newValue, client, publicPage, isSameResource }) {
     if (file !== undefined && newValue !== undefined && newValue !== file.name) {
-      const newPath = file.webDavPath.substr(1, file.webDavPath.lastIndexOf('/'))
+      const newPath = file.webDavPath.slice(1, file.webDavPath.lastIndexOf('/') + 1)
       if (publicPage) {
         return client.publicFiles
           .move(file.webDavPath, newPath + newValue, context.getters.publicLinkPassword)
diff --git a/packages/web-app-preview/src/App.vue b/packages/web-app-preview/src/App.vue
index b55bf7b4987..0ea63e8476b 100644
--- a/packages/web-app-preview/src/App.vue
+++ b/packages/web-app-preview/src/App.vue
@@ -202,7 +202,7 @@ export default {
         y: this.thumbDimensions,
         // strip double quotes from etag
         // we have no etag, e.g. on shared with others page
-        c: this.activeFilteredFile.etag?.substr(1, this.activeFilteredFile.etag.length - 2),
+        c: this.activeFilteredFile.etag?.slice(1, -1),
         scalingup: 0,
         preview: 1,
         a: 1
diff --git a/packages/web-runtime/src/components/Topbar/Notifications.vue b/packages/web-runtime/src/components/Topbar/Notifications.vue
index 3408b7e562e..4b70e7831ac 100644
--- a/packages/web-runtime/src/components/Topbar/Notifications.vue
+++ b/packages/web-runtime/src/components/Topbar/Notifications.vue
@@ -76,7 +76,7 @@ export default {
       this.$client.requests
         .ocs({
           service: 'apps/' + app,
-          action: link.substr(link.lastIndexOf('api')),
+          action: link.slice(link.lastIndexOf('api')),
           method: type
         })
         .then((res) => {
@@ -86,7 +86,7 @@ export default {
           })
           res.json().then((json) => {
             json.ocs.data.forEach((item) => {
-              const path = item.path.substr(0, item.path.lastIndexOf('/') + 1)
+              const path = item.path.slice(0, item.path.lastIndexOf('/') + 1)
               const absolutePath = this.$route.params.item ? this.$route.params.item : '/'
               if (path === absolutePath) this.reloadFilesList(path)
             })
diff --git a/rollup.config.js b/rollup.config.js
index 1877d634a39..71eff617204 100644
--- a/rollup.config.js
+++ b/rollup.config.js
@@ -148,8 +148,9 @@ const plugins = [
                 }
                 files[c].forEach((f) => {
                   const fp = path.parse(f.fileName)
+                  const lastDash = fp.name.lastIndexOf('-')
                   acc[c][
-                    production ? fp.name.substr(0, fp.name.lastIndexOf('-')) || fp.name : fp.name
+                    production ? fp.name.slice(0, lastDash !== -1 ? lastDash : 0) || fp.name : fp.name
                   ] = c === 'js' ? fp.name : f.fileName
                 })