Go: syscall/js Index | Examples | Files

package js

import "syscall/js"

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.

Index

Examples

Package Files

callback.go js.go typedarray.go

type Callback Uses

type Callback struct {
    Value // the JavaScript function that queues the callback for execution
    // contains filtered or unexported fields
}

Callback is a Go function that got wrapped for use as a JavaScript callback.

func NewCallback Uses

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.

Code:play 

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 Uses

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 (Callback) Release Uses

func (c Callback) Release()

Release frees up resources allocated for the callback. The callback must not be invoked after calling Release.

type Error Uses

type Error struct {
    // Value is the underlying JavaScript error value.
    Value
}

Error wraps a JavaScript error.

func (Error) Error Uses

func (e Error) Error() string

Error implements the error interface.

type EventCallbackFlag Uses

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 Type Uses

type Type int

Type represents the JavaScript type of a Value.

const (
    TypeUndefined Type = iota
    TypeNull
    TypeBoolean
    TypeNumber
    TypeString
    TypeSymbol
    TypeObject
    TypeFunction
)

func (Type) String Uses

func (t Type) String() string

type TypedArray Uses

type TypedArray struct {
    Value
}

TypedArray represents a JavaScript typed array.

func TypedArrayOf Uses

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 (TypedArray) Release Uses

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.

type Value Uses

type Value struct {
    // contains filtered or unexported fields
}

Value represents a JavaScript value.

func Global Uses

func Global() Value

Global returns the JavaScript global object, usually "window" or "global".

func Null Uses

func Null() Value

Null returns the JavaScript value "null".

func Undefined Uses

func Undefined() Value

Undefined returns the JavaScript value "undefined".

func ValueOf Uses

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 (Value) Bool Uses

func (v Value) Bool() bool

Bool returns the value v as a bool. It panics if v is not a JavaScript boolean.

func (Value) Call Uses

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 (Value) Float Uses

func (v Value) Float() float64

Float returns the value v as a float64. It panics if v is not a JavaScript number.

func (Value) Get Uses

func (v Value) Get(p string) Value

Get returns the JavaScript property p of value v.

func (Value) Index Uses

func (v Value) Index(i int) Value

Index returns JavaScript index i of value v.

func (Value) InstanceOf Uses

func (v Value) InstanceOf(t Value) bool

InstanceOf reports whether v is an instance of type t according to JavaScript's instanceof operator.

func (Value) Int Uses

func (v Value) Int() int

Int returns the value v truncated to an int. It panics if v is not a JavaScript number.

func (Value) Invoke Uses

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 (Value) Length Uses

func (v Value) Length() int

Length returns the JavaScript property "length" of v.

func (Value) New Uses

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 (Value) Set Uses

func (v Value) Set(p string, x interface{})

Set sets the JavaScript property p of value v to ValueOf(x).

func (Value) SetIndex Uses

func (v Value) SetIndex(i int, x interface{})

SetIndex sets the JavaScript index i of value v to ValueOf(x).

func (Value) String Uses

func (v Value) String() string

String returns the value v converted to string according to JavaScript type conversions.

func (Value) Type Uses

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.

type ValueError Uses

type ValueError struct {
    Method string
    Type   Type
}

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.

func (*ValueError) Error Uses

func (e *ValueError) Error() string

Package js imports 2 packages (graph) and is imported by 35 packages. Updated 2018-12-15. Refresh now. Tools for package owners.