cancellation

A method for making async operations cancellable

Installation

Component:

$ component install ForbesLindesay/cancellation

NPM:

$ npm install cancellation

API

$3

Returns a new CancellationTokenSource:

``javascript
var tokenSource = require('cancellation');
var source = tokenSource();
callAsyncOperation(arg1, arg2, arg3, source.token);
setTimeout(function () {
source.cancel('Operation timed out');
}, 1000);
`

$3

Returns an 'empty' CancellationToken (one that will never be cancelled).

`javascript
var tokenSource = require('cancellation');
function asyncOperation(arg1, arg2, arg3, cancellationToken) {
cancellationToken = cancellationToken || tokenSource.empty;

//Continue with function knowing there is a cancellation token
}
`

$3

Returns true if the token has been cancelled:

`javascript
//In ES6
function asyncOperation(cancellationToken) {
return spawn(function* () {
while(!cancellationToken.isCancelled()) {
yield NextAsyncOp();
}
})
}
`

$3

Throws the rejection reason if the token has been cancelled:

`javascript
//In ES6
function asyncOperation(cancellationToken) {
return spawn(function* () {
while(true) {
cancellationToken.throwIfCancelled()
yield NextAsyncOp();
}
})
}
`

$3

Calls cb when the cancellation token is cancelled (this is probably currently the most useful of these methods).

`javascript
function get(url, cancellationToken) {
var def = defer();

var req = request(url, function (err, res) {
if (err) def.reject(err);
else def.resolve(res);
});

cancellationToken
.onCancelled(function (reason) {
def.reject(reason);
req.abort();
});

return def.promise;
}
``

License

MIT