ECMAScript/JavaScript engine in pure Go



ECMAScript 5.1(+) implementation in Go.


Goja is an implementation of ECMAScript 5.1 in pure Go with emphasis on standard compliance and performance.

This project was largely inspired by otto.

Minimum required Go version is 1.14.


Known incompatibilities and caveats


WeakMap is implemented by embedding references to the values into the keys. This means that as long as the key is reachable all values associated with it in any weak maps also remain reachable and therefore cannot be garbage collected even if they are not otherwise referenced, even after the WeakMap is gone. The reference to the value is dropped either when the key is explicitly removed from the WeakMap or when the key becomes unreachable.

To illustrate this:

var m = new WeakMap();
var key = {};
var value = {/* a very large object */};
m.set(key, value);
value = undefined;
m = undefined; // The value does NOT become garbage-collectable at this point
key = undefined; // Now it does
// m.delete(key); // This would work too

The reason for it is the limitation of the Go runtime. At the time of writing (version 1.15) having a finalizer set on an object which is part of a reference cycle makes the whole cycle non-garbage-collectable. The solution above is the only reasonable way I can think of without involving finalizers. This is the third attempt (see and for more details).

Note, this does not have any effect on the application logic, but may cause a higher-than-expected memory usage.


How fast is it?

Although it's faster than many scripting language implementations in Go I have seen (for example it's 6-7 times faster than otto on average) it is not a replacement for V8 or SpiderMonkey or any other general-purpose JavaScript engine. You can find some benchmarks here.

Why would I want to use it over a V8 wrapper?

It greatly depends on your usage scenario. If most of the work is done in javascript (for example crypto or any other heavy calculations) you are definitely better off with V8.

If you need a scripting language that drives an engine written in Go so that you need to make frequent calls between Go and javascript passing complex data structures then the cgo overhead may outweigh the benefits of having a faster javascript engine.

Because it's written in pure Go there are no cgo dependencies, it's very easy to build and it should run on any platform supported by Go.

It gives you a much better control over execution environment so can be useful for research.

Is it goroutine-safe?

No. An instance of goja.Runtime can only be used by a single goroutine at a time. You can create as many instances of Runtime as you like but it's not possible to pass object values between runtimes.

Where is setTimeout()?

setTimeout() assumes concurrent execution of code which requires an execution environment, for example an event loop similar to nodejs or a browser. There is a separate project aimed at providing some NodeJS functionality, and it includes an event loop.

Can you implement (feature X from ES6 or higher)?

Some ES6 functionality has been implemented. So far this is mostly built-ins, not syntax enhancements. See for more details.

The ongoing work is done in the es6 branch which is merged into master when appropriate. Every commit in this branch represents a relatively stable state (i.e. it compiles and passes all enabled tc39 tests), however because the version of tc39 tests I use is quite old, it may be not as well tested as the ES5.1 functionality. Because ES6 is a superset of ES5.1 it should not break your existing code.

I will be adding features in their dependency order and as quickly as my time allows. Please do not ask for ETAs. Features that are open in the milestone are either in progress or will be worked on next.

How do I contribute?

Before submitting a pull request please make sure that:

  • You followed ECMA standard as close as possible. If adding a new feature make sure you've read the specification, do not just base it on a couple of examples that work fine.
  • Your change does not have a significant negative impact on performance (unless it's a bugfix and it's unavoidable)
  • It passes all relevant tc39 tests.

Current Status

  • There should be no breaking changes in the API, however it may be extended.
  • Some of the AnnexB functionality is missing.

Basic Example

Run JavaScript and get the result value.

vm := goja.New()
v, err := vm.RunString("2 + 2")
if err != nil {
if num := v.Export().(int64); num != 4 {

Passing Values to JS

Any Go value can be passed to JS using Runtime.ToValue() method. See the method's documentation for more details.

Exporting Values from JS

A JS value can be exported into its default Go representation using Value.Export() method.

Alternatively it can be exported into a specific Go variable using Runtime.ExportTo() method.

Within a single export operation the same Object will be represented by the same Go value (either the same map, slice or a pointer to the same struct). This includes circular objects and makes it possible to export them.

Calling JS functions from Go

There are 2 approaches:

vm := New()
_, err := vm.RunString(`
function sum(a, b) {
    return a+b;
if err != nil {
sum, ok := AssertFunction(vm.Get("sum"))
if !ok {
    panic("Not a function")

res, err := sum(Undefined(), vm.ToValue(40), vm.ToValue(2))
if err != nil {
// Output: 42
const SCRIPT = `
function f(param) {
    return +param + 2;

vm := New()
_, err := vm.RunString(SCRIPT)
if err != nil {

var fn func(string) string
err = vm.ExportTo(vm.Get("f"), &fn)
if err != nil {

fmt.Println(fn("40")) // note, _this_ value in the function will be undefined.
// Output: 42

The first one is more low level and allows specifying this value, whereas the second one makes the function look like a normal Go function.

Mapping struct field and method names

By default, the names are passed through as is which means they are capitalised. This does not match the standard JavaScript naming convention, so if you need to make your JS code look more natural or if you are dealing with a 3rd party library, you can use a FieldNameMapper:

vm := New()
vm.SetFieldNameMapper(TagFieldNameMapper("json", true))
type S struct {
    Field int `json:"field"`
vm.Set("s", S{Field: 42})
res, _ := vm.RunString(`s.field`) // without the mapper it would have been s.Field
// Output: 42

There are two standard mappers: TagFieldNameMapper and UncapFieldNameMapper, or you can use your own implementation.

Native Constructors

In order to implement a constructor function in Go use func (goja.ConstructorCall) *goja.Object. See Runtime.ToValue() documentation for more details.

Regular Expressions

Goja uses the embedded Go regexp library where possible, otherwise it falls back to regexp2.


Any exception thrown in JavaScript is returned as an error of type *Exception. It is possible to extract the value thrown by using the Value() method:

vm := New()
_, err := vm.RunString(`



if jserr, ok := err.(*Exception); ok {
    if jserr.Value().Export() != "Test" {
        panic("wrong value")
} else {
    panic("wrong type")

If a native Go function panics with a Value, it is thrown as a Javascript exception (and therefore can be caught):

var vm *Runtime

func Test() {

vm = New()
vm.Set("Test", Test)
_, err := vm.RunString(`

try {
} catch(e) {
    if (e !== "Error") {
        throw e;


if err != nil {


func TestInterrupt(t *testing.T) {
    const SCRIPT = `
    var i = 0;
    for (;;) {

    vm := New()
    time.AfterFunc(200 * time.Millisecond, func() {

    _, err := vm.RunString(SCRIPT)
    if err == nil {
        t.Fatal("Err is nil")
    // err is of type *InterruptError and its Value() method returns whatever has been passed to vm.Interrupt()

NodeJS Compatibility

There is a separate project aimed at providing some of the NodeJS functionality.

  • Adding native constructors

    Adding native constructors

    I've forked and started dabbling into allowing package users to create "native" constructors and instances.

    I'm implementing part of the Web API (Response, Request, Headers, etc.) and needed some way to create more complex instances that kept a state outside of goja.

    Here's my rough implementation so far:

    // constructor.go
    package goja
    type NativeFunction func(FunctionCall) Value
    type ConstructorFunction func(args []Value, inst *Object) *Object
    type Method struct {
    	call   NativeFunction
    	length int
    type Constructor struct {
    	Name string
    	r    *Runtime
    	proto  *Object
    	static *Object
    	ctor   ConstructorFunction
    	length int
    	methods map[string]Method
    func (r *Runtime) NewConstructor(name string, ctor ConstructorFunction, length int) *Constructor {
    	return &Constructor{
    		Name:    name,
    		r:       r,
    		ctor:    ctor,
    		length:  length,
    		methods: map[string]Method{},
    func (c *Constructor) createProto(val *Object) objectImpl {
    	o := &baseObject{
    		class:      c.Name,
    		val:        val,
    		extensible: true,
    	for name, method := range c.methods {
    		o._putProp(name, c.r.newNativeFunc(, nil, name, nil, method.length), true, false, true)
    	return o
    func (c *Constructor) createStatic(val *Object) objectImpl {
    	o := c.r.newNativeFuncConstructObj(val, c.ctor, c.Name, c.proto, c.length)
    	// _putProp here...
    	return o
    func (c *Constructor) NewInstance(args []Value, proto *Object) *Object {
    	bo := c.r.newBaseObject(proto, c.Name)
    	val := c.ctor(args, bo.val)
    	return val
    func (c *Constructor) Init() {
    	c.proto = c.r.newLazyObject(c.createProto)
    	c.static = c.r.newLazyObject(c.createStatic)
    	c.r.addToGlobal(c.Name, c.static)
    func (c *Constructor) DefineFunction(name string, call NativeFunction, length int) {
    	c.methods[name] = Method{call, length}

    Surprisingly, this works ok. Here's an example of how I'm using it:

    func constructResponse(vm *goja.Runtime) goja.ConstructorFunction {
    	return func(args []goja.Value, res *goja.Object) *goja.Object {
    		res.Set("body", nil)
    		res.Set("bodyUsed", false)
    		res.Set("ok", true)
    		res.Set("redirected", false)
    		res.Set("status", 200)
    		res.Set("statusText", "OK")
    		res.Set("type", "default")
    		res.Set("url", "")
    		res.Set("text", bodyText(vm, strings.NewReader("")))
    		return res
    func initResponse(vm *goja.Runtime) {
    	c := vm.NewConstructor("Response", constructResponse(vm), 2)

    This works. Except I'm left with the same issue trying to keep state around. I have to create a bunch of closures.

    For instance, for the text() function: I'd like it to keep around a io.Reader and read from it from the text() function.

    As far as I can tell, there's already a similar pattern in goja. Namely, the newDateObject function seems to create a special kind of object that embed baseObject and a few more fields. It makes sense, except that's all unexported and I'm not sure how I can make it generic enough.

    I'm mostly looking for advice on how to proceed. Ideally, from a package user's perspective, the developer would only have to provide a constructor and a struct instance to make it work.

    I think maybe abstracting and exporting a few more structures would help. I guess I'd mostly need to create a few structs embedding baseObject or implementing objectImpl.

    Any thoughts?

    opened by jeromegn 18
  • Misbehavior of ToValue() on map type with methods

    Misbehavior of ToValue() on map type with methods

    I found an issue while trying to enumerate the keys of an object that I created with ToValue() from a map type having helper methods.

    As an example, let's use http.Header type which is a Go map type with methods. When converting a http.Header value using ToValue(), this line of code in ToValue() prevents from making it a objectGoMapReflect and ends up as a objectGoReflect.

    But the its key enumeration only happens on methods and not on the map keys.

    Here is a test example that demonstrates the issue:

    	func TestMapTypeBinding(t *testing.T) {
    		headers := http.Header{
    			"k0": []string{},
    			"k1": []string{"v1"},
    			"k2": []string{"v21", "v22"},
    			"k3": []string{"v3"},
    		vm := goja.New()
    		vm.Set("headers", headers)
    		v, err := vm.RunString(`Object.keys(headers)`)
    		require.NoError(t, err)
    		result := v.Export()
    		require.Equal(t, []interface{}{"k0", "k1", "k2", "k3"}, result)

    Failing with:

    Expected :[]interface {}{"k0", "k1", "k2", "k3"} Actual :[]interface {}{"Add", "Del", "Get", "Set", "Write", "WriteSubset"}

    I'd be happy to provide a fix, but I'd like to understand first in which case it should be methods only as suggested by the current implementation.

    question wontfix 
    opened by Julio-Guerra 14
  • Multiple functions in my Javascript file

    Multiple functions in my Javascript file

    Hello, I come from Otto world and I want to migrate to this library because of very bad performance issues. I am using it for a normalisation pipeline.

    I used to put 4 or 5 functions into a JS file, and then call one of them into my Golang code.

    Example (here I call the function Exlcude) :

    // Run
    returnRaw, err := vm.Run(`Exclude(` + string(incidentJSON) + `);`)
    if err != nil {
    	return false, fmt.Errorf("Error while running the JS code : %s", err)

    How can I do this with your lib please ? Thanks a lot ! :)

    opened by fallais 12
  • ES6 Proxy (WIP)

    ES6 Proxy (WIP)

    I'm working on an ES6 Proxy implementation. Traps can be implemented in JavaScript as in the specification or using a Go struct and the specific function implementations.

    Currently still work in progress, some tests are still missing, therefore most probably doesn't work yet in all specified situations.

    Anyhow would be happy to get some feedback, as this is my first bigger change to commit back to the official goja repository :-)

    I bet there would have to be changes here and there to integrate before it can be merged eventually

    opened by noctarius 12
  • Question: how feasible is it to share Freezed objects between goja.Runtimes

    Question: how feasible is it to share Freezed objects between goja.Runtimes

    The question is more or less in the title. The specific use case is an array with objects that mostly will contain strings, numbers, or other array/objects containing the same.

    Obviously having a function and calling that function will be bad and having a regex can trigger #214, but are there such situations for the other types, and are there other things that need to be taken into account ... apart from me thinking that this is a bad idea and that w/e answer you give will change over time.

    For more context, you can look at this discussion

    opened by mstoykov 11
  • (*vm).Interrupt causes a data race

    (*vm).Interrupt causes a data race

    Per pull request #14, (*vm).Interrupt causes a data race. This results in undefined behavior and means that interrupts are currently unsafe to use. It can be resolved in the short term by using atomics (as in #14) or other explicit synchronization to signal the interrupt from a separate goroutine, and in the long term may be fixed in another manner.

    As discussed in #14, it is unacceptable for a data race to be included in a critical part of a VM, especially as part of an interrupt. According to @dop251, the data race and undefined behavior here is intentional in the pursuit of performance, and objects to the use of atomics to resolve this. The goal, then, is to find another method of causing an interrupt that both satisfies @dop251's performance requirements (currently unstated) and eliminates the data race, preferably without introducing unsafe code that cannot be checked by the race detector.

    This issue is intended to discuss other approaches to removing the interrupt data race, knowing that atomics are off the table (or somehow too slow).

    opened by nilium 11
  • Test for and fix (*vm).Interrupt data race

    Test for and fix (*vm).Interrupt data race

    This patch adds a test for a data race under (*vm).Interrupt, where an interrupt flag (boolean) is set to true inside of a lock but read outside of a lock. Since the lock is only taken at the end of (*vm).run to clear the interrupt value and un-set the interrupt flag, it doesn't make sense to lock for every check on the interrupt flag.

    I assume there's a reason for not using a channel here (even though it'd be simpler), but the most minimal change to be made right now is to replace the bool with a uint32 (or some other integer) and read/write it via atomics.

    The patch adds an (*vm).interrupted method to check the interrupt flag atomically and stores it only via atomics. The type change to uint32 also ensures that there are no other uses of the interrupt bool field (since a uint32 isn't ever treated as a bool and vice-versa). The lock remains in place to serialize setting and clearing the interrupt value.

    To test the race, checkout the first commit (73d6439) and run go test -race -run TestInterruptRace -- this should be enough to trigger it.

    opened by nilium 11
  • Structs


    type str struct { A [5]float64 B [5]float64 C [5]float64 D [5]float64 }

    func main(){ mystr:= str{ A: [5]float64{11,22,333,444,55}, B: [5]float64{11,22,333,444,55}, C: [5]float64{11,22,333,444,55}, D: [5]float64{11,22,333,444,55}, } vm.Set("mystr", mystr) var prg = "" + "mystr.A[0];" } I get a nil from this. Am I not indexing the array properly? mystr.A works fine just not mystr.A[0] access.

    'mystr.A' yields [11 22 333 444 55]

    opened by konethmelathil 10
  • Memory leaks?

    Memory leaks?


    I'm building a universal web app, where goja handles JS rendering on the server.

    Now I'm in the phase of doing performance tests, and for some reason goja seems to be leaking memory.

    I'm using to perform load tests, and after the load test it seems is holding memory and not releasing it. I'm not too sure if that's goja fault (probably not), but maybe you know anything off the top of your head how to prevent memory leaks?

    Here's the heap pprof BEFORE the load test:

    And here's the one after the load test:

    And this is the code that handles VM creation:

    Any help or suggestions will be appreciated.

    opened by iKonrad 10
  • Check if something is still running. Kill the VM?

    Check if something is still running. Kill the VM?

    Can we check if something is still running so maybe we can have a limited runtime time? So we could maybe check if the thing is finished executing? That also applies to the event loop. On top of that can we have something to just stop the execution mid-process?

    opened by JSH32 9
  • WeakMap memory leak

    WeakMap memory leak

    package gojatest
    import (
    func TestWeakMap(t *testing.T) {
    	for i := 0; i < 100; i++ {
    		r := goja.New()
    		r.RunScript("", "var x = {}; new WeakMap().set(x, {})")
    		r = nil
    	time.Sleep(100 * time.Millisecond)
    	time.Sleep(100 * time.Millisecond)
    $ go test weakmap_test.go -memprofile=/tmp/heap

    There are still tons of inuse_objects:

    Still have no idea why (it seems to be related with runtime.SetFinalizer).

    opened by lujjjh 8
  • list features in docs, that jumped over ES5.1 (ES6)

    list features in docs, that jumped over ES5.1 (ES6)

    Class has been implemented at It is great feature, thank you.

    At this time, static/private was also implemented. this goes beyond ES6. People who come later, may missed this feature(even it's a great feature.).

    Do you plan to list features that jumped over ES5.1 (ES6) in the Readme? or is it ok to contribute to the Readme?

    opened by arukiidou 2
  • Some more tests not being ran, but likely should be.

    Some more tests not being ran, but likely should be.

    Due to some tests aren't being ran.

    But I have found at least some that arguably should be. This was possible as with the classes supported added (thanks again :bow: ) the k6 tc39 tests, which run more tests than goja, are still failing for some tests and some of them seem like they should be passing.

    If you do remove it you will get the following list:

            --- FAIL: TestTC39/tc39/test/built-ins/Reflect/Symbol.toStringTag.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/prefix-decrement/S11.4.5_A6_T3.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/prefix-decrement/S11.4.5_A6_T2.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/prefix-decrement/S11.4.5_A6_T1.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/postfix-increment/S11.3.1_A6_T3.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/postfix-increment/S11.3.1_A6_T2.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/postfix-increment/S11.3.1_A6_T1.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/postfix-decrement/S11.3.2_A6_T3.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/postfix-decrement/S11.3.2_A6_T1.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/postfix-decrement/S11.3.2_A6_T2.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/prefix-increment/S11.4.4_A6_T3.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/prefix-increment/S11.4.4_A6_T2.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/prefix-increment/S11.4.4_A6_T1.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.9_T2.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.9_T4.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.9_T1.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.8_T4.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.8_T2.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.8_T1.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.7_T4.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.7_T2.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.7_T1.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.6_T4.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.6_T2.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.6_T1.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.5_T4.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.5_T2.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.5_T1.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.4_T4.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.3_T4.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.4_T1.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.4_T2.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.3_T2.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.3_T1.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.2_T4.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.2_T2.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.2_T1.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.1_T4.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.1_T2.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.11_T4.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.11_T2.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.1_T1.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.11_T1.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.10_T4.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.10_T2.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/compound-assignment/S11.13.2_A7.10_T1.js (0.00s)
            --- FAIL: TestTC39/tc39/test/language/expressions/assignment/S11.13.1_A7_T3.js (0.00s)

    All of them seem to be something that should work, and they also seem to be about the quantity or sequence of how stuff are being evaluated.

    opened by mstoykov 2
  • There is a method defined to struct pointer, how to call it from struct elem?

    There is a method defined to struct pointer, how to call it from struct elem?

    The go code is:

    type Obj struct {
    	Name string
    func (o *Obj) RunInPtr() {
    	fmt.Printf("[%s] run in ptr\r\n", o.Name)
    func (o Obj) RunInElem() {
    	fmt.Printf("[%s] run in elem\r\n", o.Name)
    func newObjPtr(name string) *Obj {
    	return &Obj{
    		Name: name,
    func newObj(name string) Obj {
    	return Obj{
    		Name: name,
    func main() {
    	engine := goja.New()
    	engine.Set("newObj", newObj)
    	engine.Set("newObjPtr", newObjPtr)
    	buff, _ := ioutil.ReadFile(os.Args[1])
    	code := string(buff)
    	v, err := engine.RunScript(os.Args[1], code)

    The test js is:

    let a = newObjPtr("ptr");
    let b = newObj("elem");

    Then I get the error:

    [ptr] run in elem
    [ptr] run in ptr
    [elem] run in elem
    TypeError: Object has no member 'RunInPtr' at test.js:7:11(27)

    PS: I have wrote a tool to import go package to goja.

    The trouble is that, some function return the struct element instead of pointer of it.

    Calling methods defined on it's pointer causes error.

    opened by garfeng 0
  • How can I capture console logs from inside VM

    How can I capture console logs from inside VM

    Hello, For some requirements, I need to return the console logs. Had it been pure javascript, I could have done something like the below : var list = []; window.console.log = (val)=>{list.push(val)} // list will now contain all the console logs inside it I tried to add a custom method like print('something here') but was unable to define it. Any help would be appreciated. Thanks

    opened by vishaNagpal 4
  • Can I interact with a JS script while it is running?

    Can I interact with a JS script while it is running?

    For example, I have a javascript game loop, I use a Go grpc server to run it.

    When the player sends an operation request, the Go grpc server will change the status of javascript game loop.

    Can I do it with goji?

    opened by HZHgagaga 0
  • Comparing primitive pointers

    Comparing primitive pointers

    Goja will convert a go pointer of a primitive type to a JS object, and this prevents this value to be triple equaled in JavaScript. From my point of view this is counterintuitive because I'd expect that *uint16(nil) would be js(undefined or null) and a non nil pointer would be just the primitive value.

    I could manually create the object via vm.NewObject(), but this would create boilerplate, which the tries to prevent.

    This issue is kinda a duplicate of #377, but I felt like it doesn't really describe the problems with this behavior. Feel free to close the issue regardless, as this probably makes the internal implementation of all primitive types more complex.

    Simple example of the behavior:

    type Thing struct {
    	X uint16  `json:"x"`
    	Y *uint16 `json:"y"`
    func main() {
    	vm := goja.New()
    	vm.SetFieldNameMapper(goja.TagFieldNameMapper("json", true))
    	x := uint16(5)
    	vm.Set("thing", Thing{
    		X: x,
    		Y: &x,
    	fmt.Println("typeof thing.y  ", mustExec(vm, "typeof thing.y").String())
    	fmt.Println("typeof thing.x  ", mustExec(vm, "typeof thing.x").String())
    	fmt.Println("thing.x === 5  ", mustExec(vm, "thing.x === 5").ToBoolean())
    	fmt.Println("thing.y === 5  ", mustExec(vm, "thing.y === 5").ToBoolean())
    	fmt.Println("thing.x === thing.y  ", mustExec(vm, "thing.x === thing.y").ToBoolean())
    	// typeof thing.y   object
    	// typeof thing.x   number
    	// thing.x === 5   true
    	// thing.y === 5   false
    	// thing.x === thing.y   false
    func mustExec(vm *goja.Runtime, s string) goja.Value {
    	v, err := vm.RunScript("myfile", s)
    	if err != nil {
    	return v
    opened by jmattheis 4
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