es6pledges
Releasable Promises for Javascript ES6
(also known as "cancellable promises")
USAGE
Pledges can be used just like Promises, with the addition of
the ability to release the pledge from it's obligation, via
resolve()
, reject()
or release()
.
Releasing a pledge results in the execution of a release function that can terminate the work, and settle the underlying Promise.
In the even that the release function cannot terminate the work,
it can optionally cancel the release and leave all of the pending
await
, then()
, catch()
handlers in place.
// a cancellable delay function
function pledgeDelay( delay ){
let timeout;
return new Pledge(
// this is the normal promise function
( resolve, reject ) => {
timeout = setTimeout( resolve, delay );
},
// this is a release/cancellation function
() => {
clearTimeout(timeout);
}
);
}
const pledge = pledgeDelay( 1000000 )
.then( value => console.log( "resolved:", value ))
.catch( reason => console.log("rejected:", reason ));
pledge.reject( "I don't want to wait that long" );
// output
//
// rejected: I don't want to wait that long
A subtle point
When a chain of pledges is released, ALL of the .then() clauses in the chain also get released.
Notice in the example above we rejected the pledge, the .catch() ran.
This also works in general, where then() causes are all resolved.
Here's another example:
const pledge = (
pledgeDelay( 1000000 )
.then( () => pledgeDelay( 1000000 ))
.then( value => console.log(
"You will see this, because it is called immediately when we", value
))
);
pledge.resolve( "release the entire pledge chain" );
// output
//
// You will see this, because it is called immediately when we release
// the entire pledge chain
API
new Pledge()
new Pledge ( pledgeFunction, releaseFunction )
Creates a new Pledge object that will settle at the completion of the pledgeFunction
or
when cancelled via the releaseFunction
pledgeFunction
a function of the form
( resolve, reject ) => {...}
that does some work, and then eventually calls eitherresolve()
orreject()
releaseFunction
a function of the form
( resolve, reject, status, reason, ...extras )
that is triggered if the Pledge is released. It should terminate any ongoign work being done by thepledgeFunction
.The arguments
status, reason, ...extra
are received from the call topledge.release()
and can be used byreleaseFunction
to determine how to settle the pledge.if
releaseFunction
does not does not settle the pledge by calling eitherresolve()
orreject()
, andreleaseFunction
returnstrue
, then the release of the pledge is cancelled.If no
releaseFunction
is provided, or ifreleaseFunction
does not settle the pledge and does not cancel the release of the pledge, then the pledge is settled via default behavior. Which isresolve( reason )
is called ifstatus
is true, andreject( reason )
is called otherwise.
Pledge.prototype.release()
pledge.release( status, reason, ...extras )
Releases a pledge from its commitment early, resulting in the
execution of the releaseFunction
provided at the creation of the
Pledge.
status, reason, ...extra
The arguments
status, reason, ...extra
are passed to `releaseFunction to determine how to settle the pledge.If no
releaseFunction
is provided, or ifreleaseFunction
does not settle the pledge and does not cancel the release of the pledge, then the pledge is settled via default behavior. Which isresolve( reason )
is called ifstatus
is true, andreject( reason )
is called otherwise.
Returns true if the pledge is settled, or false if the release was cancelled by the
releaseFunction
Pledge.prototype.resolve()
Pledge.prototype.fulfill()
pledge.resolve( reason, ...extras )
pledge.fulfill( reason, ...extras )
shorthand for pledge.release( true, reason, ...extras )
NOTE the member function
Pledge.prototype.resolve()
is different the class static functionPledge.resolve()
. The member function causes the early release of the Pledge, whereas static function returns an already resolved Pledge object
Pledge.prototype.reject()
pledge.reject( reason, ...extras )
shorthand for pledge.release( false, reason, ...extras )
NOTE the member function
Pledge.prototype.reject()
is different the class static functionPledge.reject()
. The member function causes the early release of the Pledge, whereas static function returns an already rejected Pledge object
Pledge.prototype.catch()
Pledge.prototype.finally()
Pledge.prototype.then()
Pledge.all()
Pledge.allSettled()
Pledge.any()
Pledge.race()
Pledge.reject()
Pledge.resolve()
These are identical to the Promises
equivalent