[Bug 26517] New: Methods that return promises are unable to throw exceptions


            Bug ID: 26517
           Summary: Methods that return promises are unable to throw
           Product: WebAppsWG
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: WebIDL
          Assignee: cam@mcc.id.au
          Reporter: ian@hixie.ch
        QA Contact: public-webapps-bugzilla@w3.org
                CC: mike@w3.org, public-script-coord@w3.org
            Blocks: 25662


The spec for operations says:

# If O has a return type that is a promise type, then:
#  1. Let reject be the initial value of %Promise%.reject.
#  2. Return the result of calling reject with %Promise% as the this
#     object and the exception as the single argument value.

This is bad practice, IMHO, as discussed in detail here:

If I want my API to reject the promise, then I'll reject the promise. If I want
it to throw an exception, then I should be able to throw an exception.

In particular, if an API is called with bad arguments, then the exception
should throw immediately, just like if it's name was typoed. The behaviour of:

   foo.bar(-1); // only accepts positive numbers

...should be the same as the behaviour of:

   foo.baz(1); // there's no "baz" method, it's called "bar"

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Received on Monday, 4 August 2014 18:32:10 UTC