github.com/robertkrimen/otto
Package otto is a JavaScript parser and interpreter written natively in Go.
To use import it with the following:
import (
"github.com/robertkrimen/otto"
)
Run something in the VM
vm := otto.New()
vm.Run(`
abc = 2 + 2;
console.log("The value of abc is " + abc); // 4
`)
Get a value out of the VM
if value, err := vm.Get("abc"); err == nil {
if value_int, err := value.ToInteger(); err == nil {
fmt.Printf("", value_int, err)
}
}
Set a number
vm.Set("def", 11)
vm.Run(`
console.log("The value of def is " + def);
// The value of def is 11
`)
Set a string
vm.Set("xyzzy", "Nothing happens.")
vm.Run(`
console.log(xyzzy.length); // 16
`)
Get the value of an expression
value, _ = vm.Run("xyzzy.length")
{
// value is an int64 with a value of 16
value, _ := value.ToInteger()
}
An error happens
value, err = vm.Run("abcdefghijlmnopqrstuvwxyz.length")
if err != nil {
// err = ReferenceError: abcdefghijlmnopqrstuvwxyz is not defined
// If there is an error, then value.IsUndefined() is true
...
}
Set a Go function
vm.Set("sayHello", func(call otto.FunctionCall) otto.Value {
fmt.Printf("Hello, %s.\n", call.Argument(0).String())
return otto.Value{}
})
Set a Go function that returns something useful
vm.Set("twoPlus", func(call otto.FunctionCall) otto.Value {
right, _ := call.Argument(0).ToInteger()
result, _ := vm.ToValue(2 + right)
return result
})
Use the functions in JavaScript
result, _ = vm.Run(`
sayHello("Xyzzy"); // Hello, Xyzzy.
sayHello(); // Hello, undefined
result = twoPlus(2.0); // 4
`)
A separate parser is available in the parser package if you're just interested in building an AST.
Parse and return an AST
filename := "" // A filename is optional
src := `
// Sample xyzzy example
(function(){
if (3.14159 > 0) {
console.log("Hello, World.");
return;
}
var xyzzy = NaN;
console.log("Nothing happens.");
return xyzzy;
})();
`
// Parse some JavaScript, yielding a *ast.Program and/or an ErrorList
program, err := parser.ParseFile(nil, filename, src, 0)
You can run (Go) JavaScript from the command line with otto.
go install github.com/robertkrimen/otto/otto@latest
Run JavaScript by entering some source on stdin or by giving otto a filename:
otto example.js
Optionally include the JavaScript utility-belt library, underscore, with this import:
import (
"github.com/robertkrimen/otto"
_ "github.com/robertkrimen/otto/underscore"
)
// Now every otto runtime will come loaded with underscore
For more information: underscore
The following are some limitations with otto:
use strict will parse, but does nothing.Go translates JavaScript-style regular expressions into something that is
"regexp" compatible via parser.TransformRegExp. Unfortunately, RegExp requires
backtracking for some patterns, and backtracking is not supported by Go
re2.
Therefore, the following syntax is incompatible:
(?=) // Lookahead (positive), currently a parsing error
(?!) // Lookahead (backhead), currently a parsing error
\1 // Backreference (\1, \2, \3, ...), currently a parsing error
A brief discussion of these limitations: Regexp (?!re)
More information about re2
In addition to the above, re2 (Go) has a different definition for \s: [\t\n\f\r ]. The JavaScript definition, on the other hand, also includes \v, Unicode
"Separator, Space", etc.
If you want to stop long running executions (like third-party code), you can use the interrupt channel to do this:
package main
import (
"errors"
"fmt"
"os"
"time"
"github.com/robertkrimen/otto"
)
var halt = errors.New("Stahp")
func main() {
runUnsafe(`var abc = [];`)
runUnsafe(`
while (true) {
// Loop forever
}`)
}
func runUnsafe(unsafe string) {
start := time.Now()
defer func() {
duration := time.Since(start)
if caught := recover(); caught != nil {
if caught == halt {
fmt.Fprintf(os.Stderr, "Some code took to long! Stopping after: %v\n", duration)
return
}
panic(caught) // Something else happened, repanic!
}
fmt.Fprintf(os.Stderr, "Ran code successfully: %v\n", duration)
}()
vm := otto.New()
vm.Interrupt = make(chan func(), 1) // The buffer prevents blocking
watchdogCleanup := make(chan struct{})
defer close(watchdogCleanup)
go func() {
select {
case <-time.After(2 * time.Second): // Stop after two seconds
vm.Interrupt <- func() {
panic(halt)
}
case <-watchdogCleanup:
}
close(vm.Interrupt)
}()
vm.Run(unsafe) // Here be dragons (risky code)
}
Where is setTimeout / setInterval?
These timing functions are not actually part of the ECMA-262 specification.
Typically, they belong to the window object (in the browser). It would not be
difficult to provide something like these via Go, but you probably want to wrap
otto in an event loop in that case.
For an example of how this could be done in Go with otto, see natto.
Here is some more discussion of the issue:
var ErrVersion = errors.New("version mismatch")
type Error struct {}
An Error represents a runtime error, e.g. a TypeError, a ReferenceError, etc.
func (err Error) Error() string
Error returns a description of the error
TypeError: 'def' is not a function
func (err Error) String() string
String returns a description of the error and a trace of where the error occurred.
TypeError: 'def' is not a function
at xyz (<anonymous>:3:9)
at <anonymous>:7:1/
type FunctionCall struct {
This Value
ArgumentList []Value
Otto *Otto
}
FunctionCall is an encapsulation of a JavaScript function call.
func (self FunctionCall) Argument(index int) Value
Argument will return the value of the argument at the given index.
If no such argument exists, undefined is returned.
type Object struct {}
Object is the representation of a JavaScript object.
func (self Object) Call(name string, argumentList ...interface{}) (Value, error)
Call a method on the object.
It is essentially equivalent to:
var method, _ := object.Get(name)
method.Call(object, argumentList...)
An undefined value and an error will result if:
func (self Object) Class() string
Class will return the class string of the object.
The return value will (generally) be one of:
Object
Function
Array
String
Number
Boolean
Date
RegExp
func (self Object) Get(name string) (Value, error)
Get the value of the property with the given name.
func (self Object) Keys() []string
Get the keys for the object
Equivalent to calling Object.keys on the object
func (self Object) Set(name string, value interface{}) error
Set the property of the given name to the given value.
An error will result if the setting the property triggers an exception (i.e. read-only), or there is an error during conversion of the given value.
func (self Object) Value() Value
Value will return self as a value.
type Otto struct {
// Interrupt is a channel for interrupting the runtime. You can use this to halt a long running execution, for example.
// See "Halting Problem" for more information.
Interrupt chan func()
}
Otto is the representation of the JavaScript runtime. Each instance of Otto has a self-contained namespace.
func New() *Otto
New will allocate a new JavaScript runtime
func Run(src interface{}) (*Otto, Value, error)
Run will allocate a new JavaScript runtime, run the given source on the allocated runtime, and return the runtime, resulting value, and error (if any).
src may be a string, a byte slice, a bytes.Buffer, or an io.Reader, but it MUST always be in UTF-8.
src may also be a Script.
src may also be a Program, but if the AST has been modified, then runtime behavior is undefined.
func (self Otto) Call(source string, this interface{}, argumentList ...interface{}) (Value, error)
Call the given JavaScript with a given this and arguments.
If this is nil, then some special handling takes place to determine the proper this value, falling back to a "standard" invocation if necessary (where this is undefined).
If source begins with "new " (A lowercase new followed by a space), then Call will invoke the function constructor rather than performing a function call. In this case, the this argument has no effect.
// value is a String object
value, _ := vm.Call("Object", nil, "Hello, World.")
// Likewise...
value, _ := vm.Call("new Object", nil, "Hello, World.")
// This will perform a concat on the given array and return the result
// value is [ 1, 2, 3, undefined, 4, 5, 6, 7, "abc" ]
value, _ := vm.Call(`[ 1, 2, 3, undefined, 4 ].concat`, nil, 5, 6, 7, "abc")
func (self *Otto) Compile(filename string, src interface{}) (*Script, error)
Compile will parse the given source and return a Script value or nil and an error if there was a problem during compilation.
script, err := vm.Compile("", `var abc; if (!abc) abc = 0; abc += 2; abc;`)
vm.Run(script)
func (in *Otto) Copy() *Otto
Copy will create a copy/clone of the runtime.
Copy is useful for saving some time when creating many similar runtimes.
This method works by walking the original runtime and cloning each object, scope, stash, etc. into a new runtime.
Be on the lookout for memory leaks or inadvertent sharing of resources.
func (self Otto) Get(name string) (Value, error)
Get the value of the top-level binding of the given name.
If there is an error (like the binding does not exist), then the value will be undefined.
func (self Otto) Object(source string) (*Object, error)
Object will run the given source and return the result as an object.
For example, accessing an existing object:
object, _ := vm.Object(`Number`)
Or, creating a new object:
object, _ := vm.Object(`({ xyzzy: "Nothing happens." })`)
Or, creating and assigning an object:
object, _ := vm.Object(`xyzzy = {}`)
object.Set("volume", 11)
If there is an error (like the source does not result in an object), then nil and an error is returned.
func (self Otto) Run(src interface{}) (Value, error)
Run will run the given source (parsing it first if necessary), returning the resulting value and error (if any)
src may be a string, a byte slice, a bytes.Buffer, or an io.Reader, but it MUST always be in UTF-8.
If the runtime is unable to parse source, then this function will return undefined and the parse error (nothing will be evaluated in this case).
src may also be a Script.
src may also be a Program, but if the AST has been modified, then runtime behavior is undefined.
func (self Otto) Set(name string, value interface{}) error
Set the top-level binding of the given name to the given value.
Set will automatically apply ToValue to the given value in order to convert it to a JavaScript value (type Value).
If there is an error (like the binding is read-only, or the ToValue conversion fails), then an error is returned.
If the top-level binding does not exist, it will be created.
func (self Otto) ToValue(value interface{}) (Value, error)
ToValue will convert an interface{} value to a value digestible by otto/JavaScript.
type Script struct {}
Script is a handle for some (reusable) JavaScript. Passing a Script value to a run method will evaluate the JavaScript.
func (self *Script) String() string
type Value struct {}
Value is the representation of a JavaScript value.
func FalseValue() Value
FalseValue will return a value representing false.
It is equivalent to:
ToValue(false)
func NaNValue() Value
NaNValue will return a value representing NaN.
It is equivalent to:
ToValue(math.NaN())
func NullValue() Value
NullValue will return a Value representing null.
func ToValue(value interface{}) (Value, error)
ToValue will convert an interface{} value to a value digestible by otto/JavaScript
This function will not work for advanced types (struct, map, slice/array, etc.) and you should use Otto.ToValue instead.
func TrueValue() Value
TrueValue will return a value representing true.
It is equivalent to:
ToValue(true)
func UndefinedValue() Value
UndefinedValue will return a Value representing undefined.
func (value Value) Call(this Value, argumentList ...interface{}) (Value, error)
Call the value as a function with the given this value and argument list and return the result of invocation. It is essentially equivalent to:
value.apply(thisValue, argumentList)
An undefined value and an error will result if:
func (value Value) Class() string
Class will return the class string of the value or the empty string if value is not an object.
The return value will (generally) be one of:
Object
Function
Array
String
Number
Boolean
Date
RegExp
func (self Value) Export() (interface{}, error)
Export will attempt to convert the value to a Go representation and return it via an interface{} kind.
Export returns an error, but it will always be nil. It is present for backwards compatibility.
If a reasonable conversion is not possible, then the original value is returned.
undefined -> nil (FIXME?: Should be Value{})
null -> nil
boolean -> bool
number -> A number type (int, float32, uint64, ...)
string -> string
Array -> []interface{}
Object -> map[string]interface{}
func (value Value) IsBoolean() bool
IsBoolean will return true if value is a boolean (primitive).
func (value Value) IsDefined() bool
IsDefined will return false if the value is undefined, and true otherwise.
func (value Value) IsFunction() bool
IsFunction will return true if value is a function.
func (value Value) IsNaN() bool
IsNaN will return true if value is NaN (or would convert to NaN).
func (value Value) IsNull() bool
IsNull will return true if the value is null, and false otherwise.
func (value Value) IsNumber() bool
IsNumber will return true if value is a number (primitive).
func (value Value) IsObject() bool
IsObject will return true if value is an object.
func (value Value) IsPrimitive() bool
IsPrimitive will return true if value is a primitive (any kind of primitive).
func (value Value) IsString() bool
IsString will return true if value is a string (primitive).
func (value Value) IsUndefined() bool
IsUndefined will return true if the value is undefined, and false otherwise.
func (value Value) Object() *Object
Object will return the object of the value, or nil if value is not an object.
This method will not do any implicit conversion. For example, calling this method on a string primitive value will not return a String object.
func (value Value) String() string
String will return the value as a string.
This method will make return the empty string if there is an error.
func (value Value) ToBoolean() (bool, error)
ToBoolean will convert the value to a boolean (bool).
ToValue(0).ToBoolean() => false
ToValue("").ToBoolean() => false
ToValue(true).ToBoolean() => true
ToValue(1).ToBoolean() => true
ToValue("Nothing happens").ToBoolean() => true
If there is an error during the conversion process (like an uncaught exception), then the result will be false and an error.
func (value Value) ToFloat() (float64, error)
ToFloat will convert the value to a number (float64).
ToValue(0).ToFloat() => 0.
ToValue(1.1).ToFloat() => 1.1
ToValue("11").ToFloat() => 11.
If there is an error during the conversion process (like an uncaught exception), then the result will be 0 and an error.
func (value Value) ToInteger() (int64, error)
ToInteger will convert the value to a number (int64).
ToValue(0).ToInteger() => 0
ToValue(1.1).ToInteger() => 1
ToValue("11").ToInteger() => 11
If there is an error during the conversion process (like an uncaught exception), then the result will be 0 and an error.
func (value Value) ToString() (string, error)
ToString will convert the value to a string (string).
ToValue(0).ToString() => "0"
ToValue(false).ToString() => "false"
ToValue(1.1).ToString() => "1.1"
ToValue("11").ToString() => "11"
ToValue('Nothing happens.').ToString() => "Nothing happens."
If there is an error during the conversion process (like an uncaught exception), then the result will be the empty string ("") and an error.
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