Namespace: webdriver.promise
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class Promise<T>

All implemented interfaces
IThenable<T>
webdriver.promise.Thenable<T>

Represents the eventual value of a completed operation. Each promise may be in one of three states: pending, fulfilled, or rejected. Each promise starts in the pending state and may make a single transition to either a fulfilled or rejected state, at which point the promise is considered resolved.

new Promise(resolver, opt_flow)

Parameters
resolverfunction(function(?(T|{then: ?})=): ?, function(*=): ?): ?

Function that is invoked immediately to begin computation of this promise's value. The function should accept a pair of callback functions, one for fulfilling the promise and another for rejecting it.

opt_flow?webdriver.promise.ControlFlow=

The control flow this instance was created under. Defaults to the currently active flow.

Instance Methods

cancel(opt_reason)code »

Cancels the computation of this promise's value, rejecting the promise in the process. This method is a no-op if the promise has already been resolved.

Specified by: webdriver.promise.Thenable

Parameters
opt_reason?(string|webdriver.promise.CancellationError)=

The reason this promise is being cancelled.

isPending()code »

Specified by: webdriver.promise.Thenable

Returns
boolean

Whether this promise's value is still being computed.

then(opt_callback, opt_errback)code »

Registers listeners for when this instance is resolved.

Specified by: webdriver.promise.Thenable, IThenable

Parameters
opt_callback?function(T): (R|IThenable<R>)=

The function to call if this promise is successfully resolved. The function should expect a single argument: the promise's resolved value.

opt_errback?function(*): (R|IThenable<R>)=

The function to call if this promise is rejected. The function should expect a single argument: the rejection reason.

Returns
webdriver.promise.Promise

A new promise which will be resolved with the result of the invoked callback.

thenCatch(errback)code »

Registers a listener for when this promise is rejected. This is synonymous with the catch clause in a synchronous API:

// Synchronous API:
try {
  doSynchronousWork();
} catch (ex) {
  console.error(ex);
}

// Asynchronous promise API:
doAsynchronousWork().thenCatch(function(ex) {
  console.error(ex);
});

Specified by: webdriver.promise.Thenable

Parameters
errbackfunction(*): (R|IThenable<R>)

The function to call if this promise is rejected. The function should expect a single argument: the rejection reason.

Returns
webdriver.promise.Promise

A new promise which will be resolved with the result of the invoked callback.

thenFinally(callback)code »

Registers a listener to invoke when this promise is resolved, regardless of whether the promise's value was successfully computed. This function is synonymous with the finally clause in a synchronous API:

// Synchronous API:
try {
  doSynchronousWork();
} finally {
  cleanUp();
}

// Asynchronous promise API:
doAsynchronousWork().thenFinally(cleanUp);

Note: similar to the finally clause, if the registered callback returns a rejected promise or throws an error, it will silently replace the rejection error (if any) from this promise:

try {
  throw Error('one');
} finally {
  throw Error('two');  // Hides Error: one
}

promise.rejected(Error('one'))
    .thenFinally(function() {
      throw Error('two');  // Hides Error: one
    });

Specified by: webdriver.promise.Thenable

Parameters
callbackfunction(): (R|IThenable<R>)

The function to call when this promise is resolved.

Returns
webdriver.promise.Promise

A promise that will be fulfilled with the callback result.

toString()code »

Returns
string