Throw explicit error message about bad input

Author: es128

index.js

@@ -474,6 +474,14 @@ FSWatcher.prototype.add = function(paths, _origAdd, _internal) {
   this.closed = false;
   paths = flatten(arrify(paths));
 
+  function isString(maybeString) {
+    return typeof maybeString === 'string'
+  }
+
+  if (!paths.every(isString)) {
+    throw new TypeError('Non-string provided as watch path');
+  }
+
   if (cwd) paths = paths.map(function(path) {
     if (isAbsolute(path)) {
       return path;