Philip Frank created THRIFT-4406:
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Summary: JavaScript: Use modern Promise implementations
Key: THRIFT-4406
URL: https://issues.apache.org/jira/browse/THRIFT-4406
Project: Thrift
Issue Type: Improvement
Components: JavaScript - Compiler
Reporter: Philip Frank
Priority: Minor
I would like to acces the results of service method invocations in a web
browser environment using
[Promises|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this]
(or a compatible API). I'm willing to work on the necessary changes in the
compiler and am seeking guidance regarding the best way to make these changes.
Current state:
In browser JS, i can pass a callback function as last argument when calling a
method:
{code:javascript}
service.getFoo('a1', 'a2', function(foo) {
alert(foo);
});
{code}
There is also a synchronous API, however this blocking way is discouraged by
browser vendors. It also fails with an error for me when using
WebSocketTransport instead of XHRTransport.
{code:javascript}
alert(service.getFoo('a1', 'a2'));
{code}
In JS code generated for NodeJS, the 'q' library is included, which provides an
API mostly compatible with JavaScript's native Promises.
{code:javascript}
service.getFoo('a1', 'a2').then(function(foo) {
alert(foo);
});
{code}
>From what I can tell 'q' is mostly irrelevant today since native Promises are
>supported in NodeJs [for many
>versions|http://node.green/#ES2015-built-ins-Promise].
Regarding support in browsers, native Promises work in [recent versions of most
browsers|https://caniuse.com/#feat=promises] and can be enabled in other cases
by including one of the many polyfill libraries, like the popular
[core-js|https://github.com/zloirock/core-js#ecmascript-6-promise].
Proposed solution:
In both browser and nodeJS, service methods return a Promise when invoked
without a callback. This has many advantages for developers:
* Promise API is an established standard in modern JavaScript (ECMAScript), it
is easy for developers to consume and to use with other libraries
* Error handling is possible through {{catch()}}
* Result handling is very flexible through chaining
* Promises can be combined through {{Promise.all()}} and {{Promise.race()}}
* The
[{{await}}|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/await]
keyword makes it even easier to write async code. (Support limited to some
browsers or with cross-compilers like [babel|https://babeljs.io/])
However, this would break compatibility:
* Synchronous (blocking) invocations would no longer be supported, instead a
Promise instead of the value is returned
* with NodeJS code relying on some features specific to 'q' (e.g. {{finally()}}
and {{done()`)
* Internet Explorer needs a polyfill for Promises
I'm assuming the code generated by Thrift should stay backwards compatible in
the foreseeable future, so I suggest making these changes behind a new compiler
flag, {{-gen js:es6}} (for ECMAScript 6). This would also open up the ability
to leverage more ES6 features in the future: For example, using {{const}}
instead of {{var}} might give a slight performance improvement and using the
{{class}} syntax could improve readability of the generated code.
Please share any thoughts regarding this topic or hints towards a good
implementation. If there are no objections, I'm willing to start working on
this soon, with the hopes of getting my changes accepted into the project
codebase.
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