Fix abort error when using custom request

[leiming]

The request in reqs[uid] may not get a standard instance of request while calling customRequest function which returns a Promise.

Checking abort function before being called could solve this scenario.

[coveralls]

Changes Unknown when pulling 9abb8a9 on leiming:master into ** on react-component:master**.

[coveralls]

Changes Unknown when pulling dcca820 on leiming:master into ** on react-component:master**.

[benjycui]

According to me, custom request should support abort.

[leiming]

Thank you for replying me, @benjycui

If we will support to customizing customAbort function while calling customRequest , there is no reason not to support to customizing other refer request functions which include onSuccess, onError or onProgress.

I think that abort function bind in request instance is also a feasible scheme.

[paranoidjk]

@leiming

you can help us modify the api doc, the customRequest should be () => { abort: Function }

and IMO, this PR is acceptable, more robust check before call.

[benjycui]

and IMO, this PR is acceptable, more robust check before call.

Nope, connection should be close when we don't need them.

e.g. we are uploading a big file(50MB?), then we destroy Upload. We should destroy connection, otherwise, this will occupy the network.

[benjycui]

I think this PR should be closed. @shepherdwind

you can help us modify the api doc, the customRequest should be () => { abort: Function }

cc @leiming , and you can add a warning, if the return value of customRequest is invalid.

[paranoidjk]

ok，check and warning before call is the way too，that means we think abort is not a optional interface

[benjycui]

@paranoidjk sometimes, we can swallow an error, but I don't think this error should be swallowed. So, just let it crash and print a warning, for this problem can be found easily while developing.

[leiming]

@paranoidjk @benjycui , I agree on the error should not be swallowed since abort interface is not optional but required.