isPromise() thenable fix

javascript/node/selenium-webdriver/lib/util.js

@@ -34,7 +34,16 @@ function isObject(value) {
  * @return {boolean} Whether the value is a promise.
  */
 function isPromise(value) {
-  return Object.prototype.toString.call(value) === '[object Promise]'
+  try {
+    // Use array notation so the Closure compiler does not obfuscate away our
+    // contract.
+    return (
+      (typeof value === 'object' || typeof value === 'function') &&
+      typeof value['then'] === 'function'
+    )
+  } catch (ex) {
+    return false
+  }
 }
 
 module.exports = {

javascript/node/selenium-webdriver/test/lib/promise_test.js

@@ -64,9 +64,14 @@ describe('promise', function () {
     const x = new Promise(v, v)
     const p = createRejectedPromise('reject')
     const q = Promise.resolve('resolved')
+    const t = { then() {} }
+    const f = () => {}
+    f.then = () => {}
     assert.equal(true, promise.isPromise(x))
     assert.equal(true, promise.isPromise(p))
     assert.equal(true, promise.isPromise(q))
+    assert.equal(true, promise.isPromise(t))
+    assert.equal(true, promise.isPromise(f))
     assert.equal(false, promise.isPromise(0))
     assert.equal(false, promise.isPromise(false))
     assert.equal(false, promise.isPromise(true))