Prevent loosing focus after a char composition ended by Tab key. Fix v…

…ercel#1341 (vercel#1349)

lib/hterm.js

@@ -182,11 +182,22 @@ hterm.Terminal.prototype.copySelectionToClipboard = function () {
   }
 };
 
+let lastEventTimeStamp;
+let lastEventKey;
 // passthrough all the commands that are meant to control
 // hyper and not the terminal itself
 const oldKeyDown = hterm.Keyboard.prototype.onKeyDown_;
 hterm.Keyboard.prototype.onKeyDown_ = function (e) {
   const modifierKeysConf = this.terminal.modifierKeys;
+  if (e.timeStamp === lastEventTimeStamp && e.key === lastEventKey) {
+    // Event was already processed.
+    // It seems to occur after a char composition ended by Tab and cause a blur.
+    // See https://github.com/zeit/hyper/issues/1341
+    e.preventDefault();
+    return;
+  }
+  lastEventTimeStamp = e.timeStamp;
+  lastEventKey = e.key;
 
   if (e.altKey &&
       e.which !== 16 && // Ignore other modifer keys