golang-wasm/wasm/reflect_to.go

162 lines
3.9 KiB
Go

package wasm
import (
"fmt"
"reflect"
"syscall/js"
"unsafe"
)
// ToJSValue converts a given Go value into its equivalent JS form.
//
// One special case is that complex numbers (complex64 and complex128) are converted into objects with a real and imag
// property holding a number each.
//
// A function is converted into a JS function where the function returns an error if the provided arguments do not conform
// to the Go equivalent but otherwise calls the Go function.
//
// The "this" argument of a function is always passed to the Go function if its first parameter is of type js.Value.
// Otherwise, it is simply ignored.
//
// If the last return value of a function is an error, it will be thrown in JS if it's non-nil.
// If the function returns multiple non-error values, it is converted to an array when returning to JS.
//
// It panics when a channel or a map with keys other than string and integers are passed in.
func ToJSValue(x interface{}) js.Value {
if x == nil {
return js.Null()
}
// Fast path for basic types that do not require reflection.
switch x := x.(type) {
case js.Value:
return x
case js.Wrapper:
return x.JSValue()
case bool, int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64, uintptr,
unsafe.Pointer, float32, float64, string:
return js.ValueOf(x)
case complex64:
return js.ValueOf(map[string]interface{}{
"real": real(x),
"imag": imag(x),
})
case complex128:
return js.ValueOf(map[string]interface{}{
"real": real(x),
"imag": imag(x),
})
}
value := reflect.ValueOf(x)
if value.Kind() == reflect.Ptr {
value = reflect.Indirect(value)
if !value.IsValid() {
return js.Undefined()
}
}
switch value.Kind() {
case reflect.Array, reflect.Slice:
return toJSArray(value)
case reflect.Func:
return toJSFunc(value)
case reflect.Map:
return mapToJSObject(value)
case reflect.Struct:
return structToJSObject(value)
default:
panic(fmt.Sprintf("cannot convert %T to a JS value", x))
}
}
func toJSArray(x reflect.Value) js.Value {
arrayConstructor, err := Global().Get("Array")
if err != nil {
panic("Array constructor not found")
}
array := arrayConstructor.New()
for i := 0; i < x.Len(); i++ {
array.SetIndex(i, ToJSValue(x.Index(i).Interface()))
}
return array
}
func mapToJSObject(x reflect.Value) js.Value {
objectConstructor, err := Global().Get("Object")
if err != nil {
panic("Object constructor not found")
}
obj := objectConstructor.New()
iter := x.MapRange()
for {
if !iter.Next() {
break
}
key := iter.Key()
value := iter.Value().Interface()
switch key := key.Interface().(type) {
case int:
obj.SetIndex(key, ToJSValue(value))
case int8:
obj.SetIndex(int(key), ToJSValue(value))
case int16:
obj.SetIndex(int(key), ToJSValue(value))
case int32:
obj.SetIndex(int(key), ToJSValue(value))
case int64:
obj.SetIndex(int(key), ToJSValue(value))
case uint:
obj.SetIndex(int(key), ToJSValue(value))
case uint8:
obj.SetIndex(int(key), ToJSValue(value))
case uint16:
obj.SetIndex(int(key), ToJSValue(value))
case uint32:
obj.SetIndex(int(key), ToJSValue(value))
case uint64:
obj.SetIndex(int(key), ToJSValue(value))
case uintptr:
obj.SetIndex(int(key), ToJSValue(value))
case string:
obj.Set(key, ToJSValue(value))
default:
panic(fmt.Sprintf("cannot convert %T into a JS value as its key is not a string or an integer",
x.Interface()))
}
}
return obj
}
func structToJSObject(x reflect.Value) js.Value {
objectConstructor, err := Global().Get("Object")
if err != nil {
panic("Object constructor not found")
}
obj := objectConstructor.New()
structType := x.Type()
for i := 0; i < structType.NumField(); i++ {
field := structType.Field(i)
if field.PkgPath != "" {
continue
}
name := field.Name
if tagName, ok := field.Tag.Lookup("wasm"); ok {
name = tagName
}
obj.Set(name, ToJSValue(x.Field(i).Interface()))
}
return obj
}