Package js gives access to the WebAssembly host environment when using the js/wasm architecture. Its API is based on JavaScript semantics.
This package is EXPERIMENTAL. Its current scope is only to allow tests to run, but not yet to provide a comprehensive API for users. It is exempt from the Go compatibility promise.
callback.go js.go typedarray.go
Callback is a Go function that got wrapped for use as a JavaScript callback.
type Callback struct {
Value // the JavaScript function that queues the callback for execution
// contains filtered or unexported fields
}
func NewCallback(fn func(args []Value)) Callback
NewCallback returns a wrapped callback function.
Invoking the callback in JavaScript will queue the Go function fn for execution. This execution happens asynchronously on a special goroutine that handles all callbacks and preserves the order in which the callbacks got called. As a consequence, if one callback blocks this goroutine, other callbacks will not be processed. A blocking callback should therefore explicitly start a new goroutine.
Callback.Release must be called to free up resources when the callback will not be used any more.
package main
import (
"fmt"
"syscall/js"
)
func main() {
var cb js.Callback
cb = js.NewCallback(func(args []js.Value) {
fmt.Println("button clicked")
cb.Release() // release the callback if the button will not be clicked again
})
js.Global().Get("document").Call("getElementById", "myButton").Call("addEventListener", "click", cb)
}
func NewEventCallback(flags EventCallbackFlag, fn func(event Value)) Callback
NewEventCallback returns a wrapped callback function, just like NewCallback, but the callback expects to have exactly one argument, the event. Depending on flags, it will synchronously call event.preventDefault, event.stopPropagation and/or event.stopImmediatePropagation before queuing the Go function fn for execution.
func (c Callback) Release()
Release frees up resources allocated for the callback. The callback must not be invoked after calling Release.
Error wraps a JavaScript error.
type Error struct {
// Value is the underlying JavaScript error value.
Value
}
func (e Error) Error() string
Error implements the error interface.
type EventCallbackFlag int
const (
// PreventDefault can be used with NewEventCallback to call event.preventDefault synchronously.
PreventDefault EventCallbackFlag = 1 << iota
// StopPropagation can be used with NewEventCallback to call event.stopPropagation synchronously.
StopPropagation
// StopImmediatePropagation can be used with NewEventCallback to call event.stopImmediatePropagation synchronously.
StopImmediatePropagation
) Type represents the JavaScript type of a Value.
type Type int
const (
TypeUndefined Type = iota
TypeNull
TypeBoolean
TypeNumber
TypeString
TypeSymbol
TypeObject
TypeFunction
) func (t Type) String() string
TypedArray represents a JavaScript typed array.
type TypedArray struct {
Value
}
func TypedArrayOf(slice interface{}) TypedArray TypedArrayOf returns a JavaScript typed array backed by the slice's underlying array.
The supported types are []int8, []int16, []int32, []uint8, []uint16, []uint32, []float32 and []float64. Passing an unsupported value causes a panic.
TypedArray.Release must be called to free up resources when the typed array will not be used any more.
func (a TypedArray) Release()
Release frees up resources allocated for the typed array. The typed array and its buffer must not be accessed after calling Release.
Value represents a JavaScript value.
type Value struct {
// contains filtered or unexported fields
}
func Global() Value
Global returns the JavaScript global object, usually "window" or "global".
func Null() Value
Null returns the JavaScript value "null".
func Undefined() Value
Undefined returns the JavaScript value "undefined".
func ValueOf(x interface{}) Value ValueOf returns x as a JavaScript value:
| Go | JavaScript |
| ---------------------- | ---------------------- |
| js.Value | [its value] |
| js.TypedArray | typed array |
| js.Callback | function |
| nil | null |
| bool | boolean |
| integers and floats | number |
| string | string |
| []interface{} | new array |
| map[string]interface{} | new object |
func (v Value) Bool() bool
Bool returns the value v as a bool. It panics if v is not a JavaScript boolean.
func (v Value) Call(m string, args ...interface{}) Value Call does a JavaScript call to the method m of value v with the given arguments. It panics if v has no method m. The arguments get mapped to JavaScript values according to the ValueOf function.
func (v Value) Float() float64
Float returns the value v as a float64. It panics if v is not a JavaScript number.
func (v Value) Get(p string) Value
Get returns the JavaScript property p of value v.
func (v Value) Index(i int) Value
Index returns JavaScript index i of value v.
func (v Value) InstanceOf(t Value) bool
InstanceOf reports whether v is an instance of type t according to JavaScript's instanceof operator.
func (v Value) Int() int
Int returns the value v truncated to an int. It panics if v is not a JavaScript number.
func (v Value) Invoke(args ...interface{}) Value Invoke does a JavaScript call of the value v with the given arguments. It panics if v is not a function. The arguments get mapped to JavaScript values according to the ValueOf function.
func (v Value) Length() int
Length returns the JavaScript property "length" of v.
func (v Value) New(args ...interface{}) Value New uses JavaScript's "new" operator with value v as constructor and the given arguments. It panics if v is not a function. The arguments get mapped to JavaScript values according to the ValueOf function.
func (v Value) Set(p string, x interface{}) Set sets the JavaScript property p of value v to ValueOf(x).
func (v Value) SetIndex(i int, x interface{}) SetIndex sets the JavaScript index i of value v to ValueOf(x).
func (v Value) String() string
String returns the value v converted to string according to JavaScript type conversions.
func (v Value) Type() Type
Type returns the JavaScript type of the value v. It is similar to JavaScript's typeof operator, except that it returns TypeNull instead of TypeObject for null.
A ValueError occurs when a Value method is invoked on a Value that does not support it. Such cases are documented in the description of each method.
type ValueError struct {
Method string
Type Type
}
func (e *ValueError) Error() string
© Google, Inc.
Licensed under the Creative Commons Attribution License 3.0.
https://golang.org/pkg/syscall/js/