diff --git a/static/context.js b/static/context.js
index 8d697eff8..94e1f24ae 100644
--- a/static/context.js
+++ b/static/context.js
@@ -123,7 +123,7 @@ exports.isDefined = function (value) {
 
 exports.parseQueryParams = function (locationSearch) {
   var params = {}
-  var pairs = locationSearch.substr(1).split('&')
+  var pairs = locationSearch.slice(1).split('&')
   var keyValue
 
   for (var i = 0; i < pairs.length; i++) {
diff --git a/static/karma.js b/static/karma.js
index 23081eb7f..04c7ad322 100644
--- a/static/karma.js
+++ b/static/karma.js
@@ -348,7 +348,7 @@ var socket = io(location.host, {
   reconnectionDelay: 500,
   reconnectionDelayMax: Infinity,
   timeout: BROWSER_SOCKET_TIMEOUT,
-  path: KARMA_PROXY_PATH + KARMA_URL_ROOT.substr(1) + 'socket.io',
+  path: KARMA_PROXY_PATH + KARMA_URL_ROOT.slice(1) + 'socket.io',
   'sync disconnect on unload': true,
   useNativeTimers: true
 })
@@ -565,7 +565,7 @@ exports.isDefined = function (value) {
 
 exports.parseQueryParams = function (locationSearch) {
   var params = {}
-  var pairs = locationSearch.substr(1).split('&')
+  var pairs = locationSearch.slice(1).split('&')
   var keyValue
 
   for (var i = 0; i < pairs.length; i++) {