[js] Changed io.exists() to return a rejected promise if the input va…

…lue is not

a string. This would have caught the bad test from #1827

javascript/node/selenium-webdriver/CHANGES.md

@@ -1,5 +1,7 @@
 ## v2.53.2
 
+* Changed `io.exists()` to return a rejected promise if the input path is not
+   a string
 * Deprecated `Promise#thenFinally()` - use `Promise#finally()`. The thenFinally
    shim added to the promise module in v2.53.0 will be removed in v3.0
    Sorry for the churn!

javascript/node/selenium-webdriver/io/index.js

@@ -134,7 +134,11 @@ exports.copyDir = function(src, dst, opt_exclude) {
  * @return {!Promise<boolean>} A promise for whether the file exists.
  */
 exports.exists = function(aPath) {
-  return new Promise(function(fulfill) {
+  return new Promise(function(fulfill, reject) {
+    let type = typeof aPath;
+    if (type !== 'string') {
+      reject(TypeError(`expected string path, but got ${type}`));
+    }
     fs.exists(aPath, fulfill);
   });
 };

javascript/node/selenium-webdriver/test/io_test.js

@@ -165,6 +165,12 @@ describe('io', function() {
       });
     });
 
+    it('returns a rejected promise if input value is invalid', function() {
+      return io.exists(undefined).then(
+          () => assert.fail('should have failed'),
+          e => assert.ok(e instanceof TypeError));
+    });
+
     it('works for directories', function() {
       return io.exists(dir).then(assert.ok);
     });