diff --git a/src/index.js b/src/index.js
index 30627eb..e1d5994 100644
--- a/src/index.js
+++ b/src/index.js
@@ -607,15 +607,15 @@ class TerserPlugin {
             const querySplit = filename.indexOf("?");
 
             if (querySplit >= 0) {
-              query = filename.substr(querySplit);
-              filename = filename.substr(0, querySplit);
+              query = filename.slice(querySplit);
+              filename = filename.slice(0, querySplit);
             }
 
             const lastSlashIndex = filename.lastIndexOf("/");
             const basename =
               lastSlashIndex === -1
                 ? filename
-                : filename.substr(lastSlashIndex + 1);
+                : filename.slice(lastSlashIndex + 1);
             const data = { filename, basename, query };
 
             output.commentsFilename = compilation.getPath(
diff --git a/test/helpers/readAsset.js b/test/helpers/readAsset.js
index fde3ff3..bd1ae27 100644
--- a/test/helpers/readAsset.js
+++ b/test/helpers/readAsset.js
@@ -10,7 +10,7 @@ export default (asset, compiler, stats) => {
   const queryStringIdx = targetFile.indexOf("?");
 
   if (queryStringIdx >= 0) {
-    targetFile = targetFile.substr(0, queryStringIdx);
+    targetFile = targetFile.slice(0, queryStringIdx);
   }
 
   try {