From 392b175abfa19fe9566dd7908fec69cd45144b77 Mon Sep 17 00:00:00 2001
From: Chan Wen Xu <lutherchanpublic@gmail.com>
Date: Sat, 20 Mar 2021 18:56:02 +0800
Subject: [PATCH] feat: Implement a type-safe Object struct

---
 wasm/go.mod    |   3 ++
 wasm/object.go | 142 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 145 insertions(+)
 create mode 100644 wasm/go.mod
 create mode 100644 wasm/object.go

diff --git a/wasm/go.mod b/wasm/go.mod
new file mode 100644
index 0000000..31e956b
--- /dev/null
+++ b/wasm/go.mod
@@ -0,0 +1,3 @@
+module gitea.teamortix.com/Team-Ortix/go-mod-wasm/wasm
+
+go 1.16
diff --git a/wasm/object.go b/wasm/object.go
new file mode 100644
index 0000000..f1c3fe5
--- /dev/null
+++ b/wasm/object.go
@@ -0,0 +1,142 @@
+package wasm
+
+import (
+	"fmt"
+	"syscall/js"
+)
+
+// TypeMismatchError is returned when a function is called with a js.Value that has the incorrect type.
+type TypeMismatchError struct {
+	Expected js.Type
+	Actual   js.Type
+}
+
+func (e TypeMismatchError) Error() string {
+	return fmt.Sprintf("expected %v type, got %v type instead", e.Expected, e.Actual)
+}
+
+// Global returns the global object as a Object.
+// If the global object is not an object, it panics.
+func Global() Object {
+	global, err := NewObject(js.Global())
+	if err != nil {
+		panic(err)
+	}
+	return global
+}
+
+// Object is a statically typed Object instance of js.Value.
+// It should be instantiated with NewObject where it is checked for type instead of directly.
+// Calling methods on a zero Object is undefined behaviour.
+type Object struct {
+	value js.Value
+}
+
+// NewObject instantiates a new Object with the provided js.Value.
+// If the js.Value is not an Object, it returns a TypeMismatchError.
+func NewObject(raw js.Value) (Object, error) {
+	if raw.Type() != js.TypeObject {
+		return Object{}, TypeMismatchError{
+			Expected: js.TypeObject,
+			Actual:   raw.Type(),
+		}
+	}
+
+	return Object{raw}, nil
+}
+
+// Get recursively gets the Object's properties, returning a TypeMismatchError if it encounters a non-object while
+// descending through the object.
+func (o Object) Get(path ...string) (js.Value, error) {
+	current := o.value
+	for _, v := range path {
+		if current.Type() != js.TypeObject {
+			return js.Value{}, TypeMismatchError{
+				Expected: js.TypeObject,
+				Actual:   current.Type(),
+			}
+		}
+
+		current = current.Get(v)
+	}
+	return current, nil
+}
+
+// Expect is a helper function that calls Get and checks the type of the final result.
+// It returns a TypeMismatchError if a non-object is encountered while descending the path or the final type does not
+// match with the provided expected type.
+func (o Object) Expect(expectedType js.Type, path ...string) (js.Value, error) {
+	value, err := o.Get(path...)
+	if err != nil {
+		return js.Value{}, err
+	}
+
+	if value.Type() != expectedType {
+		return js.Value{}, TypeMismatchError{
+			Expected: expectedType,
+			Actual:   value.Type(),
+		}
+	}
+
+	return value, nil
+}
+
+// Delete removes property p from the object.
+func (o Object) Delete(p string) {
+	o.value.Delete(p)
+}
+
+// Equal checks if the object is equal to another value.
+// It is equivalent to JS's === operator.
+func (o Object) Equal(v js.Value) bool {
+	return o.value.Equal(v)
+}
+
+// Index indexes into the object.
+func (o Object) Index(i int) js.Value {
+	return o.value.Index(i)
+}
+
+// InstanceOf implements the instanceof operator in JavaScript.
+// If t is not a constructor, this function returns false.
+func (o Object) InstanceOf(t js.Value) bool {
+	if t.Type() != js.TypeFunction {
+		return false
+	}
+	return o.value.InstanceOf(t)
+}
+
+// JSValue implements the js.Wrapper interface.
+func (o Object) JSValue() js.Value {
+	return o.value
+}
+
+// Length returns the "length" property of the object.
+func (o Object) Length() int {
+	return o.value.Length()
+}
+
+// Set sets the property p to the value of js.ValueOf(x).
+func (o Object) Set(p string, x interface{}) {
+	o.value.Set(p, x)
+}
+
+// SetIndex sets the index i to the value of js.ValueOf(x).
+func (o Object) SetIndex(i int, x interface{}) {
+	o.value.SetIndex(i, x)
+}
+
+// String returns the object marshalled as a JSON string for debugging purposes.
+func (o Object) String() string {
+	stringify, err := Global().Expect(js.TypeFunction, "JSON", "stringify")
+	if err != nil {
+		panic(err)
+	}
+
+	jsonStr := stringify.Invoke(o)
+	if jsonStr.Type() != js.TypeString {
+		panic("JSON.stringify returned a " + jsonStr.Type().String())
+	}
+
+	return jsonStr.String()
+}