siyuan-note/siyuan · error

globalThis.Object.seal is not a function

Error message

globalThis.Object.seal is not a function

What it means

ObjectSeal resolves globalThis.Object and requires its "seal" property to be a callable function. If Object exists but Object.seal was replaced by a non-function value, goja.AssertFunction fails and this error is thrown. It indicates the Object built-in was partially overwritten or incompletely stubbed.

Source

Thrown at kernel/plugin/sandbox.go:148

	freeze, ok := goja.AssertFunction(Object.Get("freeze"))
	if !ok {
		return fmt.Errorf("globalThis.Object.freeze is not a function")
	}

	_, err := freeze(Object, obj)
	return err
}

// ObjectSeal calls Object.seal() on the given goja object.
func ObjectSeal(rt *goja.Runtime, obj *goja.Object) error {
	Object := rt.GlobalObject().Get("Object").ToObject(rt)
	if Object == nil {
		return fmt.Errorf("globalThis.Object is not an object")
	}

	seal, ok := goja.AssertFunction(Object.Get("seal"))
	if !ok {
		return fmt.Errorf("globalThis.Object.seal is not a function")
	}

	_, err := seal(Object, obj)
	return err
}

// ObjectSetDataMethods attaches text(), json(), buffer() and arrayBuffer() methods to a JS object,
// each returning a Promise that resolves with the corresponding representation of data.
func ObjectSetDataMethods(p *KernelPlugin, rt *goja.Runtime, object *goja.Object, data []byte) (err error) {
	defer func() {
		if r := recover(); r != nil {
			err = fmt.Errorf("ObjectSetDataMethods: %v", r)
		}
	}()

	lo.Must0(object.Set("text", rt.ToValue(func(call goja.FunctionCall, rt *goja.Runtime) goja.Value {
		promise, resolve, reject := rt.NewPromise()

View on GitHub (pinned to 8641553a1f)

Solutions

  1. Restore globalThis.Object.seal to a function before injection
  2. Seal API objects before untrusted code runs so built-ins cannot be overwritten first
  3. In tests, stub with a callable: Object.seal = (o) => o
  4. Catch the error and degrade gracefully (skip sealing) rather than failing plugin load

Example fix

// before
rt.RunString("Object.seal = undefined")
plugin.ObjectSeal(rt, obj) // error: not a function
// after
rt.RunString("Object.seal = Object.seal || ((o) => o)")
Defensive patterns

Strategy: type-guard

Validate before calling

o := rt.GlobalObject().Get("Object")
if o != nil {
    if _, ok := goja.AssertFunction(o.ToObject(rt).Get("seal")); !ok { /* skip or restore */ }
}

Type guard

func canSeal(rt *goja.Runtime) bool {
    o := rt.GlobalObject().Get("Object")
    if o == nil { return false }
    _, ok := goja.AssertFunction(o.ToObject(rt).Get("seal"))
    return ok
}

Try / catch

if err := plugin.ObjectSeal(rt, obj); err != nil {
    logging.LogWarningf("seal skipped: %v", err)
}

Prevention

When it happens

Trigger: Calling ObjectSeal on a runtime where globalThis.Object.seal was reassigned to undefined, a number, an object, or a non-callable value — typically by plugin code, a polyfill, or an incorrect test stub.

Common situations: Test doubles that stubbed Object.seal as a plain value; polyfills redefining Object wholesale; hardening scripts that replaced seal with metadata instead of a function.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

AI-assisted analysis of siyuan-note/siyuan@8641553a1f (2026-09-11). Data as JSON: /api/errors/a9c90c5f37f4a7de. Report an issue: GitHub.