Return self on 0 arguments, and ignore args > 2

Author: Rob Figueiredo

promise.go

@@ -100,16 +100,15 @@ func (p *Promise) Then(cbs ...FunctionCallback) *Promise {
 
 var ptr C.ValuePtr
 switch len(cbs) {
+case 0:
+return p
 case 1:
 cbID := p.ctx.iso.registerCallback(cbs[0])
 ptr = C.PromiseThen(p.ptr, C.int(cbID))
-case 2:
+default:
 cbID1 := p.ctx.iso.registerCallback(cbs[0])
 cbID2 := p.ctx.iso.registerCallback(cbs[1])
 ptr = C.PromiseThen2(p.ptr, C.int(cbID1), C.int(cbID2))
-
-default:
-panic("1 or 2 callbacks required")
 }
 return &Promise{&Object{&Value{ptr, p.ctx}}}
 }

promise_test.go

@@ -79,6 +79,7 @@ func TestPromiseRejected(t *testing.T) {
 thenInfo = info
 return nil
 }).
+Then().
 Then(
 func(_ *v8go.FunctionCallbackInfo) *v8go.Value {
 then2Fulfilled = true