Consolidate Then & Then2 by making Then variadic.

Author: Rob Figueiredo

promise.go

@@ -86,29 +86,31 @@ func (p *Promise) Result() *Value {
 return val
 }
 
-// Then invokes the given function when the promise has been fulfilled, not rejected.
-//
+// Then accepts 1 or 2 callbacks.
+// The first is invoked when the promise has been fulfilled.
+// The second is invoked when the promise has been rejected.
 // The returned Promise resolves after the callback finishes execution.
 //
 // V8 only invokes the callback when processing "microtasks".
 // The default MicrotaskPolicy processes them when the call depth decreases to 0.
 // Call (*Context).PerformMicrotaskCheckpoint to trigger it manually.
-func (p *Promise) Then(cb FunctionCallback) *Promise {
+func (p *Promise) Then(cbs ...FunctionCallback) *Promise {
 p.ctx.register()
 defer p.ctx.deregister()
-cbID := p.ctx.iso.registerCallback(cb)
-ptr := C.PromiseThen(p.ptr, C.int(cbID))
-return &Promise{&Object{&Value{ptr, p.ctx}}}
-}
 
-// Then2 invokes one of the given functions when the promise is fulfilled or rejected.
-// See Then for other details.
-func (p *Promise) Then2(onFulfilled, onRejected FunctionCallback) *Promise {
-p.ctx.register()
-defer p.ctx.deregister()
-onFulfilledID := p.ctx.iso.registerCallback(onFulfilled)
-onRejectedID := p.ctx.iso.registerCallback(onRejected)
-ptr := C.PromiseThen2(p.ptr, C.int(onFulfilledID), C.int(onRejectedID))
+var ptr C.ValuePtr
+switch len(cbs) {
+case 1:
+cbID := p.ctx.iso.registerCallback(cbs[0])
+ptr = C.PromiseThen(p.ptr, C.int(cbID))
+case 2:
+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

@@ -79,7 +79,7 @@ func TestPromiseRejected(t *testing.T) {
 thenInfo = info
 return nil
 }).
-Then2(
+Then(
 func(_ *v8go.FunctionCallbackInfo) *v8go.Value {
 then2Fulfilled = true
 return nil