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promise.go
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promise.go
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// Copyright 2021 Roger Chapman and the v8go contributors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
package v8go
// #include <stdlib.h>
// #include "v8go.h"
import "C"
import (
"errors"
)
// PromiseState is the state of the Promise.
type PromiseState int
const (
Pending PromiseState = iota
Fulfilled
Rejected
)
// PromiseResolver is the resolver object for the promise.
// Most cases will create a new PromiseResolver and return
// the associated Promise from the resolver.
type PromiseResolver struct {
*Object
prom *Promise
}
// Promise is the JavaScript promise object defined in ES6
type Promise struct {
*Object
}
// NewPromiseResolver creates a new Promise resolver for the given context.
// The associated Promise will be in a Pending state.
func NewPromiseResolver(ctx *Context) (*PromiseResolver, error) {
if ctx == nil {
return nil, errors.New("v8go: Context is required")
}
rtn := C.NewPromiseResolver(ctx.ptr)
obj, err := objectResult(ctx, rtn)
if err != nil {
return nil, err
}
return &PromiseResolver{obj, nil}, nil
}
// GetPromise returns the associated Promise object for this resolver.
// The Promise object is unique to the resolver and returns the same object
// on multiple calls.
func (r *PromiseResolver) GetPromise() *Promise {
if r.prom == nil {
ptr := C.PromiseResolverGetPromise(r.ptr)
val := &Value{ptr, r.ctx}
r.prom = &Promise{&Object{val}}
}
return r.prom
}
// Resolve invokes the Promise resolve state with the given value.
// The Promise state will transition from Pending to Fulfilled.
func (r *PromiseResolver) Resolve(val Valuer) bool {
return C.PromiseResolverResolve(r.ptr, val.value().ptr) != 0
}
// Reject invokes the Promise reject state with the given value.
// The Promise state will transition from Pending to Rejected.
func (r *PromiseResolver) Reject(err *Value) bool {
return C.PromiseResolverReject(r.ptr, err.ptr) != 0
}
// State returns the current state of the Promise.
func (p *Promise) State() PromiseState {
return PromiseState(C.PromiseState(p.ptr))
}
// Result is the value result of the Promise. The Promise must
// NOT be in a Pending state, otherwise may panic. Call promise.State()
// to validate state before calling for the result.
func (p *Promise) Result() *Value {
ptr := C.PromiseResult(p.ptr)
val := &Value{ptr, p.ctx}
return val
}
// 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(cbs ...FunctionCallback) *Promise {
cbwes := make([]FunctionCallbackWithError, len(cbs))
for i, cb := range cbs {
cb := cb
cbwes[i] = func(info *FunctionCallbackInfo) (*Value, error) {
return cb(info), nil
}
}
return p.ThenWithError(cbwes...)
}
func (p *Promise) ThenWithError(cbs ...FunctionCallbackWithError) *Promise {
var rtn C.RtnValue
switch len(cbs) {
case 1:
cbID := p.ctx.iso.registerCallback(cbs[0])
rtn = C.PromiseThen(p.ptr, C.int(cbID))
case 2:
cbID1 := p.ctx.iso.registerCallback(cbs[0])
cbID2 := p.ctx.iso.registerCallback(cbs[1])
rtn = C.PromiseThen2(p.ptr, C.int(cbID1), C.int(cbID2))
default:
panic("1 or 2 callbacks required")
}
obj, err := objectResult(p.ctx, rtn)
if err != nil {
panic(err) // TODO: Return error
}
return &Promise{obj}
}
// Catch invokes the given function if the promise is rejected.
// See Then for other details.
func (p *Promise) Catch(cb FunctionCallback) *Promise {
return p.CatchWithError(func(info *FunctionCallbackInfo) (*Value, error) {
return cb(info), nil
})
}
func (p *Promise) CatchWithError(cb FunctionCallbackWithError) *Promise {
cbID := p.ctx.iso.registerCallback(cb)
rtn := C.PromiseCatch(p.ptr, C.int(cbID))
obj, err := objectResult(p.ctx, rtn)
if err != nil {
panic(err) // TODO: Return error
}
return &Promise{obj}
}