diff --git a/src/display/dom_utils.js b/src/display/dom_utils.js
index 2caecba9a..7a1b8f2d7 100644
--- a/src/display/dom_utils.js
+++ b/src/display/dom_utils.js
@@ -461,65 +461,57 @@ function isExternalLinkTargetSet() {
   }
 }
 
-var StatTimer = (function StatTimerClosure() {
-  function rpad(str, pad, length) {
-    while (str.length < length) {
-      str += pad;
-    }
-    return str;
-  }
-  function StatTimer() {
+class StatTimer {
+  constructor(enable = true) {
     this.started = Object.create(null);
     this.times = [];
-    this.enabled = true;
+    this.enabled = !!enable;
   }
-  StatTimer.prototype = {
-    time: function StatTimer_time(name) {
-      if (!this.enabled) {
-        return;
+
+  time(name) {
+    if (!this.enabled) {
+      return;
+    }
+    if (name in this.started) {
+      warn('Timer is already running for ' + name);
+    }
+    this.started[name] = Date.now();
+  }
+
+  timeEnd(name) {
+    if (!this.enabled) {
+      return;
+    }
+    if (!(name in this.started)) {
+      warn('Timer has not been started for ' + name);
+    }
+    this.times.push({
+      'name': name,
+      'start': this.started[name],
+      'end': Date.now(),
+    });
+    // Remove timer from started so it can be called again.
+    delete this.started[name];
+  }
+
+  toString() {
+    let times = this.times;
+    // Find the longest name for padding purposes.
+    let out = '', longest = 0;
+    for (let i = 0, ii = times.length; i < ii; ++i) {
+      let name = times[i]['name'];
+      if (name.length > longest) {
+        longest = name.length;
       }
-      if (name in this.started) {
-        warn('Timer is already running for ' + name);
-      }
-      this.started[name] = Date.now();
-    },
-    timeEnd: function StatTimer_timeEnd(name) {
-      if (!this.enabled) {
-        return;
-      }
-      if (!(name in this.started)) {
-        warn('Timer has not been started for ' + name);
-      }
-      this.times.push({
-        'name': name,
-        'start': this.started[name],
-        'end': Date.now(),
-      });
-      // Remove timer from started so it can be called again.
-      delete this.started[name];
-    },
-    toString: function StatTimer_toString() {
-      var i, ii;
-      var times = this.times;
-      var out = '';
-      // Find the longest name for padding purposes.
-      var longest = 0;
-      for (i = 0, ii = times.length; i < ii; ++i) {
-        var name = times[i]['name'];
-        if (name.length > longest) {
-          longest = name.length;
-        }
-      }
-      for (i = 0, ii = times.length; i < ii; ++i) {
-        var span = times[i];
-        var duration = span.end - span.start;
-        out += rpad(span['name'], ' ', longest) + ' ' + duration + 'ms\n';
-      }
-      return out;
-    },
-  };
-  return StatTimer;
-})();
+    }
+    for (let i = 0, ii = times.length; i < ii; ++i) {
+      let span = times[i];
+      let duration = span.end - span.start;
+      out += `${span['name'].padEnd(longest)} ${duration}ms\n`;
+    }
+    return out;
+  }
+}
 
 export {
   CustomStyle,