v8

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 Go to latest Published: Dec 4, 2020 License: MIT Imports: 13 Imported by: 0

README

V8 Bindings for Go Build Status Go Report Card GoDoc

The v8 bindings allow a user to execute javascript from within a go executable.

The bindings are tested to work with several recent v8 builds matching the Chrome builds 54 - 60 (see the .travis.yml file for specific versions). For example, Chrome 59 (dev branch) uses v8 5.9.211.4 when this was written.

Note that v8 releases match the Chrome release timeline: Chrome 48 corresponds to v8 4.8.*, Chrome 49 matches v8 4.9.*. You can see the table of current chrome and the associated v8 releases at:

http://omahaproxy.appspot.com/

Using a pre-compiled v8

v8 is very slow to compile, it's a large project. If you want to go that route, there are building instructions below.

Fortunately, there's a project that pre-builds v8 for various platforms. It's packaged as a ruby gem called libv8.

# Find the appropriate gem version for your OS,
# visit: https://rubygems.org/gems/libv8/versions

# Download the gem
# MacOS Sierra is darwin-16, for v8 6.3.292.48.1 it looks like:
curl https://rubygems.org/downloads/libv8-6.3.292.48.1-x86_64-darwin-16.gem > libv8.gem

# Extract the gem (it's a tarball)
tar -xf libv8.gem

# Extract the `data.tar.gz` within
cd libv8-6.3.292.48.1-x86_64-darwin-16
tar -xzf data.tar.gz

# Symlink the compiled libraries and includes
ln -s $(pwd)/data/vendor/v8/include $GOPATH/src/github.com/augustoroman/v8/include
ln -s $(pwd)/data/vendor/v8/out/x64.release $GOPATH/src/github.com/augustoroman/v8/libv8

# Run the tests to make sure everything works
cd $GOPATH/src/github.com/augustoroman/v8
go test

Using docker (linux only)

For linux builds, you can use pre-built libraries or build your own.

Pre-built versions

To use a pre-built library, select the desired v8 version from https://hub.docker.com/r/augustoroman/v8-lib/tags/ and then run:

# Select the v8 version to use:
export V8_VERSION=6.7.77
docker pull augustoroman/v8-lib:$V8_VERSION           # Download the image, updating if necessary.
docker rm v8 ||:                                      # Cleanup from before if necessary.
docker run --name v8 augustoroman/v8-lib:$V8_VERSION  # Run the image to provide access to the files.
docker cp v8:/v8/include include/                     # Copy the include files.
docker cp v8:/v8/lib libv8/                           # Copy the library fiels.

Build your own via docker

This takes a lot longer, but is still easy:

export V8_VERSION=6.7.77
docker build --build-arg V8_VERSION=$V8_VERSION --tag augustoroman/v8-lib:$V8_VERSION docker-v8-lib/

and then extract the files as above:

docker rm v8 ||:                                      # Cleanup from before if necessary.
docker run --name v8 augustoroman/v8-lib:$V8_VERSION  # Run the image to provide access to the files.
docker cp v8:/v8/include include/                     # Copy the include files.
docker cp v8:/v8/lib libv8/                           # Copy the library fiels.

Building v8

Prep

You need to build v8 statically and place it in a location cgo knows about. This requires special tooling and a build directory. Using the official instructions as a guide, the general steps of this process are:

  1. go get the binding library (this library)
  2. Create a v8 build directory
  3. Install depot tools
  4. Configure environment
  5. Download v8
  6. Build v8
  7. Copy or symlink files to the go library path
  8. Build the bindings
go get github.com/augustoroman/v8
export V8_GO=$GOPATH/src/github.com/augustoroman/v8
export V8_BUILD=$V8_GO/v8/build #or wherever you like
mkdir -p $V8_BUILD
cd $V8_BUILD
git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
export PATH=$PATH:$V8_BUILD/depot_tools
fetch v8 #pull down v8 (this will take some time)
cd v8
git checkout 6.7.77
gclient sync

Linux

./build/install-build-deps.sh #only needed once
gn gen out.gn/golib --args="strip_debug_info=true v8_use_external_startup_data=false v8_enable_i18n_support=false v8_enable_gdbjit=false v8_static_library=true symbol_level=0 v8_experimental_extra_library_files=[] v8_extra_library_files=[]"
ninja -C out.gn/golib
# go get some coffee

OSX

gn gen out.gn/golib --args="is_official_build=true strip_debug_info=true v8_use_external_startup_data=false v8_enable_i18n_support=false v8_enable_gdbjit=false v8_static_library=true symbol_level=0 v8_experimental_extra_library_files=[] v8_extra_library_files=[]"
ninja -C out.gn/golib
# go get some coffee

Symlinking

Now you can create symlinks so that cgo can associate the v8 binaries with the go library.

cd $V8_GO
./symlink.sh $V8_BUILD/v8

Verifying

You should be done! Try running go test

Reference

Also relevant is the v8 API release changes doc:

https://docs.google.com/document/d/1g8JFi8T_oAE_7uAri7Njtig7fKaPDfotU6huOa1alds/edit

Credits

This work is based off of several existing libraries:

Documentation

Overview

Package v8 provides a Go API for the the V8 javascript engine.

This allows running javascript within a go executable. The bindings have been tested with v8 builds between 5.1.281.16 through 6.7.77.

V8 provides two main concepts for managing javascript state: Isolates and Contexts. An isolate represents a single-threaded javascript engine that can manage one or more contexts. A context is a sandboxed javascript execution environment.

Thus, if you have one isolate, you could safely execute independent code in many different contexts created in that isolate. The code in the various contexts would not interfere with each other, however no more than one context would ever be executing at a given time.

If you have multiple isolates, they may be executing in separate threads simultaneously.

This work is based off of several existing libraries:

Example 
package main

import (
	"fmt"

	v8 "github.com/cloudinaryltd/v8"
)

func main() {
	// Easy-peasy to create a new VM:
	ctx := v8.NewIsolate().NewContext()

	// You can load your js from a file, create it dynamically, whatever.
	ctx.Eval(`
            // This is javascript code!
            add = (a,b)=>{ return a + b }; // whoa, ES6 arrow functions.
        `, "add.js") // <-- supply filenames for stack traces

	// State accumulates in a context.  Add still exists.
	// The last statements' value is returned to Go.
	res, _ := ctx.Eval(`add(3,4)`, "compute.js") // don't ignore errors!
	fmt.Println("add(3,4) =", res.String())      // I hope it's 7.

	// You can also bind Go functions to javascript:
	product := func(in v8.CallbackArgs) (*v8.Value, error) {
		var result float64 = 1
		for _, arg := range in.Args {
			result *= arg.Float64()
		}
		return in.Context.Create(result) // ctx.Create is great for mapping Go -> JS.
	}
	cnt := ctx.Bind("product_function", product)
	ctx.Global().Set("product", cnt)

	res, _ = ctx.Eval(`
            // Now we can call that function in JS
            product(1,2,3,4,5)
        `, "compute2.js")

	fmt.Println("product(1,2,3,4,5) =", res.Int64())

	_, err := ctx.Eval(`
            // Sometimes there's a mistake in your js code:
            functin broken(a,b) { return a+b; }
        `, "ooops.js")
	fmt.Println("Err:", err) // <-- get nice error messages

}

Output:

add(3,4) = 7
product(1,2,3,4,5) = 120
Err: Uncaught exception: SyntaxError: Unexpected identifier
at ooops.js:3:20
              functin broken(a,b) { return a+b; }
                      ^^^^^^
Stack trace: SyntaxError: Unexpected identifier
Example (Microtasks) 
package main

import (
	"fmt"

	v8 "github.com/cloudinaryltd/v8"
)

func main() {
	// Microtasks are automatically run when the Eval'd js code has finished but
	// before Eval returns.

	ctx := v8.NewIsolate().NewContext()

	// Register a simple log function in js.
	ctx.Global().Set("log", ctx.Bind("log", func(in v8.CallbackArgs) (*v8.Value, error) {
		fmt.Println("log>", in.Arg(0).String())
		return nil, nil
	}))

	// Run some javascript that schedules microtasks, like promises.
	output, err := ctx.Eval(`
        log('start');
        let p = new Promise(resolve => { // this is called immediately
            log('resolve:5');
            resolve(5);
        });
        log('promise created');
        p.then(v => log('then:'+v));     // this is scheduled in a microtask
        log('done');                     // this is run before the microtask
        'xyz'                            // this is the output of the script
    `, "microtasks.js")

	fmt.Println("output:", output)
	fmt.Println("err:", err)

}

Output:

log> start
log> resolve:5
log> promise created
log> done
log> then:5
output: xyz
err: <nil>

Index

Examples

Constants

This section is empty.

Variables

View Source 
var Version = struct{ Major, Minor, Build, Patch int }{
	Major: int(C.version.Major),
	Minor: int(C.version.Minor),
	Build: int(C.version.Build),
	Patch: int(C.version.Patch),
}

Version exposes the compiled-in version of the linked V8 library. This can be used to test for specific javascript functionality support (e.g. ES6 destructuring isn't supported before major version 5.).

Functions

This section is empty.

Types

type Callback 

type Callback func(CallbackArgs) (*Value, error)

Callback is the signature for callback functions that are registered with a V8 context via Bind(). Never return a Value from a different V8 isolate. A return value of nil will return "undefined" to javascript. Returning an error will throw an exception. Panics are caught and returned as errors to avoid disrupting the cgo stack.

type CallbackArgs 

type CallbackArgs struct {
	Caller  Loc
	Args    []*Value
	Context *Context
}

CallbackArgs provide the context for handling a javascript callback into go. Caller is the script location that javascript is calling from. If the function is called directly from Go (e.g. via Call()), then "Caller" will be empty. Args are the arguments provided by the JS code. Context is the V8 context that initiated the call.

func (*CallbackArgs) Arg 

func (c *CallbackArgs) Arg(n int) *Value

Arg returns the specified argument or "undefined" if it doesn't exist.

type Context 

type Context struct {
	// contains filtered or unexported fields
}

Context is a sandboxed js environment with its own set of built-in objects and functions. Values and javascript operations within a context are visible only within that context unless the Go code explicitly moves values from one context to another.

func (*Context) Bind 

func (ctx *Context) Bind(name string, cb Callback) *Value

Bind creates a V8 function value that calls a Go function when invoked. This value is created but NOT visible in the Context until it is explicitly passed to the Context (either via a .Set() call or as a callback return value).

The name that is provided is the name of the defined javascript function, and generally doesn't affect anything. That is, for a call such as: 

val, _ = ctx.Bind("my_func_name", callback)

then val is a function object in javascript, so calling val.String() (or calling .toString() on the object within the JS VM) would result in: 

function my_func_name() { [native code] }

NOTE: Once registered, a callback function will be stored in the Context until it is GC'd, so each Bind for a given context will take up a little more memory each time. Normally this isn't a problem, but many many Bind's on a Context can gradually consume memory.

Example 
package main

import (
	"fmt"
	"strconv"

	v8 "github.com/cloudinaryltd/v8"
)

// AddAllNumbers is the callback function that we'll make accessible the JS VM.
// It will accept 2 or more numbers and return the sum. If fewer than two args
// are passed or any of the args are not parsable as numbers, it will fail.
func AddAllNumbers(in v8.CallbackArgs) (*v8.Value, error) {
	if len(in.Args) < 2 {
		return nil, fmt.Errorf("add requires at least 2 numbers, but got %d args", len(in.Args))
	}
	result := 0.0
	for i, arg := range in.Args {
		n, err := strconv.ParseFloat(arg.String(), 64)
		if err != nil {
			return nil, fmt.Errorf("Arg %d [%q] cannot be parsed as a number: %v", i, arg.String(), err)
		}
		result += n
	}
	return in.Context.Create(result)
}

func main() {
	ctx := v8.NewIsolate().NewContext()

	// First, we'll bind our callback function into a *v8.Value that we can
	// use as we please. The string "my_add_function" here is the used by V8 as
	// the name of the function. That is, we've defined:
	//   val.toString() = (function my_add_function() { [native code] });
	// However the name "my_add_function" isn't actually accessible in the V8
	// global scope anywhere yet.
	val := ctx.Bind("my_add_function", AddAllNumbers)

	// Next we'll set that value into the global context to make it available to
	// the JS.
	if err := ctx.Global().Set("add", val); err != nil {
		panic(err)
	}

	// Now we'll call it!
	result, err := ctx.Eval(`add(1,2,3,4,5)`, `example.js`)
	if err != nil {
		panic(err)
	}
	fmt.Println(`add(1,2,3,4,5) =`, result)

}

Output:

add(1,2,3,4,5) = 15

func (*Context) Create 

func (ctx *Context) Create(val interface{}) (*Value, error)

Create maps Go values into corresponding JavaScript values. This value is created but NOT visible in the Context until it is explicitly passed to the Context (either via a .Set() call or as a callback return value).

Create can automatically map the following types of values:

  • bool
  • all integers and floats are mapped to JS numbers (float64)
  • strings
  • maps (keys must be strings, values must be convertible)
  • time.Time values (converted to js Date object)
  • structs (exported field values must be convertible)
  • slices of convertible types
  • pointers to any convertible field
  • v8.Callback function (automatically bind'd)
  • *v8.Value (returned as-is)

Any nil pointers are converted to undefined in JS.

Values for elements in maps, structs, and slices may be any of the above types.

When structs are being converted, any fields with json struct tags will respect the json naming entry. For example: 

var x = struct {
   Ignored     string `json:"-"`
   Renamed     string `json:"foo"`
   DefaultName string `json:",omitempty"`
   Bar         string
}{"a", "b", "c", "d"}

will be converted as: 

{
    foo: "a",
    DefaultName: "b",
    Bar: "c",
}

Also, embedded structs (or pointers-to-structs) will get inlined.

Byte slices tagged as 'v8:"arraybuffer"' will be converted into a javascript ArrayBuffer object for more efficient conversion. For example: 

var y = struct {
    Buf     []byte `v8:"arraybuffer"`
}{[]byte{1,2,3}}

will be converted as 

{
   Buf: new Uint8Array([1,2,3]).buffer
}
Example (Basic) 
package main

import (
	"fmt"

	v8 "github.com/cloudinaryltd/v8"
)

func main() {
	ctx := v8.NewIsolate().NewContext()

	type Info struct{ Name, Email string }

	val, _ := ctx.Create(map[string]interface{}{
		"num":    3.7,
		"str":    "simple string",
		"bool":   true,
		"struct": Info{"foo", "bar"},
		"list":   []int{1, 2, 3},
	})

	// val is now a *v8.Value that is associated with ctx but not yet accessible
	// from the javascript scope.

	_ = ctx.Global().Set("created_value", val)

	res, _ := ctx.Eval(`
            created_value.struct.Name = 'John';
            JSON.stringify(created_value.struct)
        `, `test.js`)
	fmt.Println(res)

}

Output:

{"Name":"John","Email":"bar"}
Example (Callbacks) 
package main

import (
	"fmt"

	v8 "github.com/cloudinaryltd/v8"
)

func main() {
	ctx := v8.NewIsolate().NewContext()

	// A typical use of Create is to return values from callbacks:
	var nextId int
	getNextIdCallback := func(in v8.CallbackArgs) (*v8.Value, error) {
		nextId++
		return ctx.Create(nextId) // Return the created corresponding v8.Value or an error.
	}

	// Because Create will use reflection to map a Go value to a JS object, it
	// can also be used to easily bind a complex object into the JS VM.
	resetIdsCallback := func(in v8.CallbackArgs) (*v8.Value, error) {
		nextId = 0
		return nil, nil
	}
	myIdAPI, _ := ctx.Create(map[string]interface{}{
		"next":  getNextIdCallback,
		"reset": resetIdsCallback,
		// Can also include other stuff:
		"my_api_version": "v1.2",
	})

	// now let's use those two callbacks and the api value:
	_ = ctx.Global().Set("ids", myIdAPI)
	var res *v8.Value
	res, _ = ctx.Eval(`ids.my_api_version`, `test.js`)
	fmt.Println(`ids.my_api_version =`, res)
	res, _ = ctx.Eval(`ids.next()`, `test.js`)
	fmt.Println(`ids.next() =`, res)
	res, _ = ctx.Eval(`ids.next()`, `test.js`)
	fmt.Println(`ids.next() =`, res)
	res, _ = ctx.Eval(`ids.reset(); ids.next()`, `test.js`)
	fmt.Println(`ids.reset()`)
	fmt.Println(`ids.next() =`, res)

}

Output:

ids.my_api_version = v1.2
ids.next() = 1
ids.next() = 2
ids.reset()
ids.next() = 1

func (*Context) Eval 

func (ctx *Context) Eval(jsCode, filename string) (*Value, error)

Eval runs the javascript code in the VM. The filename parameter is informational only -- it is shown in javascript stack traces.

func (*Context) Global 

func (ctx *Context) Global() *Value

Global returns the JS global object for this context, with properties like Object, Array, JSON, etc.

func (*Context) ParseJson 

func (ctx *Context) ParseJson(json string) (*Value, error)

ParseJson uses V8's JSON.parse to parse the string and return the parsed object.

func (*Context) Terminate 

func (ctx *Context) Terminate()

Terminate will interrupt any processing going on in the context. This may be called from any goroutine.

type HeapStatistics 

type HeapStatistics struct {
	TotalHeapSize           uint64
	TotalHeapSizeExecutable uint64
	TotalPhysicalSize       uint64
	TotalAvailableSize      uint64
	UsedHeapSize            uint64
	HeapSizeLimit           uint64
	MallocedMemory          uint64
	PeakMallocedMemory      uint64
	DoesZapGarbage          bool
}

HeapStatistics represent v8::HeapStatistics which are statistics about the heap memory usage.

type Isolate 

type Isolate struct {
	// contains filtered or unexported fields
}

Isolate represents a single-threaded V8 engine instance. It can run multiple independent Contexts and V8 values can be freely shared between the Contexts, however only one context will ever execute at a time.

func NewIsolate 

func NewIsolate() *Isolate

NewIsolate creates a new V8 Isolate.

func NewIsolateWithSnapshot 

func NewIsolateWithSnapshot(s *Snapshot) *Isolate

NewIsolateWithSnapshot creates a new V8 Isolate using the supplied Snapshot to initialize all Contexts created from this Isolate.

func (*Isolate) GetHeapStatistics 

func (i *Isolate) GetHeapStatistics() HeapStatistics

GetHeapStatistics gets statistics about the heap memory usage.

func (*Isolate) NewContext 

func (i *Isolate) NewContext() *Context

NewContext creates a new, clean V8 Context within this Isolate.

func (*Isolate) SendLowMemoryNotification 

func (i *Isolate) SendLowMemoryNotification()

SendLowMemoryNotification sends an optional notification that the system is running low on memory. V8 uses these notifications to attempt to free memory.

func (*Isolate) Terminate 

func (i *Isolate) Terminate()

Terminate will interrupt all operation in this Isolate, interrupting any Contexts that are executing. This may be called from any goroutine at any time.

type Kind 

type Kind uint8

Kind is an underlying V8 representation of a *Value. Javascript values may have multiple underyling kinds. For example, a function will be both KindObject and KindFunction. 

const (
	KindUndefined Kind = iota
	KindNull
	KindName
	KindString
	KindSymbol
	KindFunction
	KindArray
	KindObject
	KindBoolean
	KindNumber
	KindExternal
	KindInt32
	KindUint32
	KindDate
	KindArgumentsObject
	KindBooleanObject
	KindNumberObject
	KindStringObject
	KindSymbolObject
	KindNativeError
	KindRegExp
	KindAsyncFunction
	KindGeneratorFunction
	KindGeneratorObject
	KindPromise
	KindMap
	KindSet
	KindMapIterator
	KindSetIterator
	KindWeakMap
	KindWeakSet
	KindArrayBuffer
	KindArrayBufferView
	KindTypedArray
	KindUint8Array
	KindUint8ClampedArray
	KindInt8Array
	KindUint16Array
	KindInt16Array
	KindUint32Array
	KindInt32Array
	KindFloat32Array
	KindFloat64Array
	KindDataView
	KindSharedArrayBuffer
	KindProxy
	KindWebAssemblyCompiledModule
)

func (Kind) String 

func (k Kind) String() string

type Loc 

type Loc struct {
	Funcname, Filename string
	Line, Column       int
}

Loc defines a script location.

type PromiseState 

type PromiseState uint8

PromiseState defines the state of a promise: either pending, resolved, or rejected. Promises that are pending have no result value yet. A promise that is resolved has a result value, and a promise that is rejected has a result value that is usually the error. 

const (
	PromiseStatePending PromiseState = iota
	PromiseStateResolved
	PromiseStateRejected
)

func (PromiseState) String 

func (s PromiseState) String() string

type Snapshot 

type Snapshot struct {
	// contains filtered or unexported fields
}

Snapshot contains the stored VM state that can be used to quickly recreate a new VM at that particular state.

Example 
package main

import (
	"fmt"

	v8 "github.com/cloudinaryltd/v8"
)

func main() {
	snapshot := v8.CreateSnapshot(`
        // Concantenate all the scripts you want at startup, e.g. lodash, etc.
        _ = { map: function() { /* ... */ }, etc: "etc, etc..." };
        // Setup my per-context global state:
        myGlobalState = {
            init: function() { this.initialized = true; },
            foo: 3,
        };
        // Run some functions:
        myGlobalState.init();
    `)
	iso := v8.NewIsolateWithSnapshot(snapshot)

	// Create a context with the state from the snapshot:
	ctx1 := iso.NewContext()
	fmt.Println("Context 1:")
	val, _ := ctx1.Eval("myGlobalState.foo = 37; myGlobalState.initialized", "")
	fmt.Println("myGlobalState.initialized:", val)
	val, _ = ctx1.Eval("myGlobalState.foo", "")
	fmt.Println("myGlobalState.foo:", val)

	// In the second context, the global state is reset to the state at the
	// snapshot:
	ctx2 := iso.NewContext()
	fmt.Println("Context 2:")
	val, _ = ctx2.Eval("myGlobalState.foo", "")
	fmt.Println("myGlobalState.foo:", val)

}

Output:

Context 1:
myGlobalState.initialized: true
myGlobalState.foo: 37
Context 2:
myGlobalState.foo: 3

func CreateSnapshot 

func CreateSnapshot(js string) *Snapshot

CreateSnapshot creates a new Snapshot after running the supplied JS code. Because Snapshots cannot have refences to external code (no Go callbacks), all of the initialization code must be pure JS and supplied at once as the arg to this function.

func RestoreSnapshotFromExport 

func RestoreSnapshotFromExport(data []byte) *Snapshot

RestoreSnapshotFromExport creates a Snapshot from a byte slice that should have previous come from Snapshot.Export().

func (*Snapshot) Export 

func (s *Snapshot) Export() []byte

Export returns the VM state data as a byte slice.

type Value 

type Value struct {
	// contains filtered or unexported fields
}

Value represents a handle to a value within the javascript VM. Values are associated with a particular Context, but may be passed freely between Contexts within an Isolate.

func (*Value) Bool 

func (v *Value) Bool() bool

Bool returns this Value as a boolean. If the underlying value is not a boolean, it will be coerced to a boolean using Javascript's coercion rules.

func (*Value) Bytes 

func (v *Value) Bytes() []byte

Bytes returns a byte slice extracted from this value when the value is of type ArrayBuffer. The returned byte slice is copied from the underlying buffer, so modifying it will not be reflected in the VM. Values of other types return nil.

func (*Value) Call 

func (v *Value) Call(this *Value, args ...*Value) (*Value, error)

Call this value as a function. If this value is not a function, this will fail.

func (*Value) Date 

func (v *Value) Date() (time.Time, error)

Date returns this Value as a time.Time. If the underlying value is not a KindDate, this will return an error.

func (*Value) Float64 

func (v *Value) Float64() float64

Float64 returns this Value as a float64. If this value is not a number, then NaN will be returned.

func (*Value) Get 

func (v *Value) Get(name string) (*Value, error)

Get a field from the object. If this value is not an object, this will fail.

func (*Value) GetIndex 

func (v *Value) GetIndex(idx int) (*Value, error)

Get the value at the specified index. If this value is not an object or an array, this will fail.

func (*Value) Int64 

func (v *Value) Int64() int64

Int64 returns this Value as an int64. If this value is not a number, then 0 will be returned.

func (*Value) IsKind 

func (v *Value) IsKind(k Kind) bool

IsKind will test whether the underlying value is the specified JS kind. The kind of a value is set when the value is created and will not change.

func (*Value) MarshalJSON 

func (v *Value) MarshalJSON() ([]byte, error)

MarshalJSON implements the json.Marshaler interface using the JSON.stringify function from the VM to serialize the value and fails if that cannot be found.

Note that JSON.stringify will ignore function values. For example, this JS object: 

{ foo: function() { return "x" }, bar: 3 }

will serialize to this: 

{"bar":3}

func (*Value) New 

func (v *Value) New(args ...*Value) (*Value, error)

New creates a new instance of an object using this value as its constructor. If this value is not a function, this will fail.

func (*Value) PromiseInfo 

func (v *Value) PromiseInfo() (PromiseState, *Value, error)

PromiseInfo will return information about the promise if this value's underlying kind is KindPromise, otherwise it will return an error. If there is no error, then the returned value will depend on the promise state: 

pending: nil
fulfilled: the value of the promise
rejected: the rejected result, usually a JS error

func (*Value) Set 

func (v *Value) Set(name string, value *Value) error

Set a field on the object. If this value is not an object, this will fail.

func (*Value) SetIndex 

func (v *Value) SetIndex(idx int, value *Value) error

SetIndex sets the object's value at the specified index. If this value is not an object or an array, this will fail.

func (*Value) String 

func (v *Value) String() string

String returns the string representation of the value using the ToString() method. For primitive types this is just the printable value. For objects, this is "[object Object]". Functions print the function definition.

Notes

Bugs

Source Files

View all Source files

Directories

Path Synopsis
cmd
v8-runjs
v8-runjs is a command-line tool to run javascript.
 v8-runjs is a command-line tool to run javascript.
Package v8console provides a simple console implementation to allow JS to log messages.
 Package v8console provides a simple console implementation to allow JS to log messages.

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