143 lines
3.6 KiB
Go
143 lines
3.6 KiB
Go
package wasm
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import (
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"fmt"
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"syscall/js"
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)
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// TypeMismatchError is returned when a function is called with a js.Value that has the incorrect type.
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type TypeMismatchError struct {
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Expected js.Type
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Actual js.Type
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}
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func (e TypeMismatchError) Error() string {
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return fmt.Sprintf("expected %v type, got %v type instead", e.Expected, e.Actual)
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}
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// Global returns the global object as a Object.
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// If the global object is not an object, it panics.
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func Global() Object {
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global, err := NewObject(js.Global())
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if err != nil {
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panic(err)
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}
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return global
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}
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// Object is a statically typed Object instance of js.Value.
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// It should be instantiated with NewObject where it is checked for type instead of directly.
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// Calling methods on a zero Object is undefined behaviour.
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type Object struct {
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value js.Value
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}
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// NewObject instantiates a new Object with the provided js.Value.
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// If the js.Value is not an Object, it returns a TypeMismatchError.
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func NewObject(raw js.Value) (Object, error) {
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if raw.Type() != js.TypeObject {
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return Object{}, TypeMismatchError{
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Expected: js.TypeObject,
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Actual: raw.Type(),
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}
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}
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return Object{raw}, nil
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}
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// Get recursively gets the Object's properties, returning a TypeMismatchError if it encounters a non-object while
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// descending through the object.
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func (o Object) Get(path ...string) (js.Value, error) {
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current := o.value
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for _, v := range path {
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if current.Type() != js.TypeObject {
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return js.Value{}, TypeMismatchError{
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Expected: js.TypeObject,
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Actual: current.Type(),
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}
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}
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current = current.Get(v)
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}
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return current, nil
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}
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// Expect is a helper function that calls Get and checks the type of the final result.
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// It returns a TypeMismatchError if a non-object is encountered while descending the path or the final type does not
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// match with the provided expected type.
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func (o Object) Expect(expectedType js.Type, path ...string) (js.Value, error) {
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value, err := o.Get(path...)
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if err != nil {
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return js.Value{}, err
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}
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if value.Type() != expectedType {
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return js.Value{}, TypeMismatchError{
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Expected: expectedType,
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Actual: value.Type(),
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}
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}
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return value, nil
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}
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// Delete removes property p from the object.
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func (o Object) Delete(p string) {
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o.value.Delete(p)
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}
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// Equal checks if the object is equal to another value.
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// It is equivalent to JS's === operator.
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func (o Object) Equal(v js.Value) bool {
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return o.value.Equal(v)
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}
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// Index indexes into the object.
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func (o Object) Index(i int) js.Value {
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return o.value.Index(i)
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}
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// InstanceOf implements the instanceof operator in JavaScript.
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// If t is not a constructor, this function returns false.
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func (o Object) InstanceOf(t js.Value) bool {
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if t.Type() != js.TypeFunction {
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return false
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}
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return o.value.InstanceOf(t)
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}
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// JSValue implements the js.Wrapper interface.
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func (o Object) JSValue() js.Value {
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return o.value
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}
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// Length returns the "length" property of the object.
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func (o Object) Length() int {
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return o.value.Length()
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}
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// Set sets the property p to the value of js.ValueOf(x).
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func (o Object) Set(p string, x interface{}) {
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o.value.Set(p, x)
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}
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// SetIndex sets the index i to the value of js.ValueOf(x).
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func (o Object) SetIndex(i int, x interface{}) {
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o.value.SetIndex(i, x)
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}
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// String returns the object marshalled as a JSON string for debugging purposes.
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func (o Object) String() string {
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stringify, err := Global().Expect(js.TypeFunction, "JSON", "stringify")
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if err != nil {
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panic(err)
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}
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jsonStr := stringify.Invoke(o)
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if jsonStr.Type() != js.TypeString {
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panic("JSON.stringify returned a " + jsonStr.Type().String())
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}
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return jsonStr.String()
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}
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