V8PromiseFactory

V8 has support for ES6 Promises and they make a clean JS-side API. So why not create promises from PHP, (later on) being resolved by PHP?

V8Js doesn’t allow direct creation of JS objects from PHP-code, a little JS-side helper needs to be used. One possibility is this:

class V8PromiseFactory
{
    private $v8;

    public function __construct(V8Js $v8)
    {
        $this->v8 = $v8;
    }

    public function __invoke($executor)
    {
        $trampoline = $this->v8->executeString(
            '(function(executor) { return new Promise(executor); })');
        return $trampoline($executor);
    }
}

… it can be used to construct an API method that returns a Promise like this:

$v8 = new V8Js();
$promiseFactory = new V8PromiseFactory($v8);

$v8->theApiCall = function() use ($promiseFactory) {
    return $promiseFactory(function($resolve, $reject) {
        // do something (maybe async) here, finally call $resolve or $reject
        $resolve(42);
    });
};

$v8->executeString("
    const p = PHP.theApiCall();
    p.then(function(result) {
        var_dump(result);
    });
");

this code

• initializes V8, V8Js and the V8PromiseFactory first
• then attaches an API call named theApiCall, that uses $promiseFactory and passes it an executor that immediately resolves to the integer 42.
• then executes some JavaScript code that uses the theApiCall function and attaches a then function that simply echos the value (42)

V8PromiseFactory::__invoke should cache $trampoline if it is used to create a lot of promises.

This code requires V8Js with pull request #219 applied to function properly.