diff --git a/bin/update_fonts.js b/bin/update_fonts.js
index e3c9788d..b15fcda6 100644
--- a/bin/update_fonts.js
+++ b/bin/update_fonts.js
@@ -8,7 +8,7 @@ const dir = 'styles/fontello';
 for(const file of fs.readdirSync(dir)) {
 	if ( file.endsWith('.css') ) {
 		const old_path = path.join(dir, file),
-			new_path = `${old_path.substr(0, old_path.length - 4)}.scss`;
+			new_path = `${old_path.slice(0, -4)}.scss`;
 
 		fs.renameSync(old_path, new_path);
 	}
diff --git a/src/modules/chat/tokenizers.jsx b/src/modules/chat/tokenizers.jsx
index 8e43cdc2..91526a50 100644
--- a/src/modules/chat/tokenizers.jsx
+++ b/src/modules/chat/tokenizers.jsx
@@ -400,7 +400,7 @@ export const Mentions = {
 						this.applyHighlight(msg, priority, null, 'mention', true);
 
 					// Push the remaining text from the token.
-					text.push(segment.substr(match[0].length));
+					text.push(segment.slice(match[0].length));
 
 				} else
 					text.push(segment);
diff --git a/src/modules/main_menu/components/profile-manager.vue b/src/modules/main_menu/components/profile-manager.vue
index cbf9fdc4..34648c0e 100644
--- a/src/modules/main_menu/components/profile-manager.vue
+++ b/src/modules/main_menu/components/profile-manager.vue
@@ -543,7 +543,7 @@ export default {
 				if ( values )
 					for(const [key, value] of Object.entries(values)) {
 						if ( key.startsWith(prefix) ) {
-							prof.set(key.substr(prefix.length), value);
+							prof.set(key.slice(prefix.length), value);
 							i++;
 						}
 					}
diff --git a/src/settings/components/page.vue b/src/settings/components/page.vue
index 248a3ffc..d6e4e448 100644
--- a/src/settings/components/page.vue
+++ b/src/settings/components/page.vue
@@ -104,7 +104,7 @@ export default {
 					out.push({
 						key: part.name,
 						i18n: `settings.filter.page.route.${this.route.name}.${part.name}`,
-						title: name[0].toLocaleUpperCase() + name.substr(1),
+						title: name[0].toLocaleUpperCase() + name.slice(1),
 						optional: part.optional
 					});
 				}
diff --git a/src/settings/context.js b/src/settings/context.js
index 4c224628..08577815 100644
--- a/src/settings/context.js
+++ b/src/settings/context.js
@@ -277,7 +277,7 @@ export default class SettingsContext extends EventEmitter {
 		if ( prefix && this._context_objects.has(prefix) ) {
 			for(const key of Object.keys(this._context) )
 				if ( key.startsWith(prefix) ) {
-					const partial_key = key.substr(prefix.length);
+					const partial_key = key.slice(prefix.length);
 					if ( ! keys.includes(partial_key) )
 						keys.push(partial_key);
 				}
diff --git a/src/settings/index.js b/src/settings/index.js
index be5f4d77..027bb46b 100644
--- a/src/settings/index.js
+++ b/src/settings/index.js
@@ -671,7 +671,7 @@ export default class SettingsManager extends Module {
 		// If we're still here, it means an individual setting was changed.
 		// Look up the profile it belongs to and emit a changed event from
 		// that profile, thus notifying any contexts or UI instances.
-		key = key.substr(2);
+		key = key.slice(2);
 
 		// Is it a value?
 		const idx = key.indexOf(':');
diff --git a/webpack.web.prod.js b/webpack.web.prod.js
index a442395a..e4be2884 100644
--- a/webpack.web.prod.js
+++ b/webpack.web.prod.js
@@ -54,7 +54,7 @@ module.exports = merge(common, {
 			publicPath: '',
 			map: data => {
 				if ( data.name.endsWith('.scss') )
-					data.name = `${data.name.substr(0,data.name.length - 5)}.css`;
+					data.name = `${data.name.slice(0, -5)}.css`;
 
 				return data;
 			}