PromisEs3

Introduction

PromisEs3 is a implementation of Promise/A+ for ES3. Its single-file and dependence-free features are designed for maximum compatibility, which is important when buiding/packing/moduling tools are not available or old browsers (like IE6) need to be considered.

This Promise implemented by this project have passed the Promise/A+ test.

Although the basic part are written in pure ES3 syntax and functions, it can make use of some ES3+ or non-standard function to obtain additional performance.

Usage

Include by <script> Tag

You can

• Directly include the Promise.js file (relatively large-sized).

• Include the compressed file promises3.min.js. Can be downloaded from Release.

When included by <script> tag, it will act as an polyfill, which means that create the Promise class in the global scope when it dosen't exist.

As Module

When PromisEs3 are imported as a module, it directly exports the the Promise class.

Can be used as:

• As Node.js (+ CommonJS) + npm module

  1. Download by npm as promises3 package.
  2. Include as module promises3 (require("promises3")).

• AMD module.

• CMD module.

Known Issue

• As most of the Promise implementation, the Promise.prototype.toString are directly inherited from Object.prototype.toString and not have been overwritten. Only when Symbol.toStringTag is available, the result of promise.toString() and Object.prototype.toString.call(promise) is guaranteed to be "[object Promise]".

• When the iterable protocol is not available, Promise.all, Promise.allSettled an other static functions takes ArrayLike as Iterable.

• On the branch with-any, a static function Promise.any is implemented. An Exception class called AggregateError which is needed by Promise.any is also implemented and exported. However, they cannot be fully polyfilled under ES5. As these 2 features are still in working draft (see MDN) and not be included in any main-stream browsers, using it is strongly deprecated.

Notice

• Some properties of the Promise object has keys embraced by "[[]]". These properties should be seen as private properties and should not be modified externally.

• In some ES3 browsers, if a object member's key is a JavaScript keyword, accessing it by operator . is not allowed. You can use promise["catch"] and promise["finally"] instead of promise.catch and promise.finally. Some tools, like babel/plugin-transform-member-expression-literals may help you covert these codes automatically.

License and Copyright

MIT Licence. See LICENSE.md.

Copyright (c) 2020 Yichen Liu.