otto: github.com/robertkrimen/otto Index | Files | Directories

package otto

import "github.com/robertkrimen/otto"

Package otto is a JavaScript parser and interpreter written natively in Go.

http://godoc.org/github.com/robertkrimen/otto

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

value, err := vm.Get("abc")
	value, _ := value.ToInteger()
}

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
`)

Parser

A separate parser is available in the parser package if you're just interested in building an AST.

http://godoc.org/github.com/robertkrimen/otto/parser

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)

otto

You can run (Go) JavaScript from the commandline with: http://github.com/robertkrimen/otto/tree/master/otto

$ go get -v github.com/robertkrimen/otto/otto

Run JavaScript by entering some source on stdin or by giving otto a filename:

$ otto example.js

underscore

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: http://github.com/robertkrimen/otto/tree/master/underscore

Caveat Emptor

The following are some limitations with otto:

* "use strict" will parse, but does nothing.
* The regular expression engine (re2/regexp) is not fully compatible with the ECMA5 specification.
* Otto targets ES5. ES6 features (eg: Typed Arrays) are not supported.

Regular Expression Incompatibility

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 the standard Go engine: https://code.google.com/p/re2/wiki/Syntax

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)" https://groups.google.com/forum/?fromgroups=#%21topic/golang-nuts/7qgSDWPIh_E

More information about re2: https://code.google.com/p/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.

Halting Problem

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

    go func() {
        time.Sleep(2 * time.Second) // Stop after two seconds
        vm.Interrupt <- func() {
            panic(halt)
        }
    }()

    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 `windows` 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:

http://github.com/robertkrimen/natto

Here is some more discussion of the issue:

* http://book.mixu.net/node/ch2.html

* http://en.wikipedia.org/wiki/Reentrancy_%28computing%29

* http://aaroncrane.co.uk/2009/02/perl_safe_signals/

Index

Package Files

builtin.go builtin_array.go builtin_boolean.go builtin_date.go builtin_error.go builtin_function.go builtin_json.go builtin_math.go builtin_number.go builtin_object.go builtin_regexp.go builtin_string.go clone.go cmpl.go cmpl_evaluate.go cmpl_evaluate_expression.go cmpl_evaluate_statement.go cmpl_parse.go console.go dbg.go error.go evaluate.go global.go inline.go object.go object_class.go otto.go otto_.go property.go result.go runtime.go scope.go script.go stash.go type_arguments.go type_array.go type_boolean.go type_date.go type_error.go type_function.go type_go_array.go type_go_map.go type_go_slice.go type_go_struct.go type_number.go type_reference.go type_regexp.go type_string.go value.go value_boolean.go value_number.go value_primitive.go value_string.go

Variables

var ErrVersion = errors.New("version mismatch")

func Run Uses

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.

type Context Uses

type Context struct {
    Filename   string
    Line       int
    Column     int
    Callee     string
    Symbols    map[string]Value
    This       Value
    Stacktrace []string
}

Context is a structure that contains information about the current execution context.

type Error Uses

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

An Error represents a runtime error, e.g. a TypeError, a ReferenceError, etc.

func (Error) Error Uses

func (err Error) Error() string

Error returns a description of the error

TypeError: 'def' is not a function

func (Error) String Uses

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 Uses

type FunctionCall struct {
    This         Value
    ArgumentList []Value
    Otto         *Otto
    // contains filtered or unexported fields
}

FunctionCall is an encapsulation of a JavaScript function call.

func (FunctionCall) Argument Uses

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.

func (FunctionCall) CallerLocation Uses

func (self FunctionCall) CallerLocation() string

CallerLocation will return file location information (file:line:pos) where this function is being called.

type Object Uses

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

Object is the representation of a JavaScript object.

func (Object) Call Uses

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:

1. There is an error during conversion of the argument list
2. The property is not actually a function
3. An (uncaught) exception is thrown

func (Object) Class Uses

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 (Object) Get Uses

func (self Object) Get(name string) (Value, error)

Get the value of the property with the given name.

func (Object) Keys Uses

func (self Object) Keys() []string

Keys gets the keys for the given object.

Equivalent to calling Object.keys on the object.

func (Object) KeysByParent Uses

func (self Object) KeysByParent() [][]string

KeysByParent gets the keys (and those of the parents) for the given object, in order of "closest" to "furthest".

func (Object) Set Uses

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 (Object) Value Uses

func (self Object) Value() Value

Value will return self as a value.

type Otto Uses

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()
    // contains filtered or unexported fields
}

Otto is the representation of the JavaScript runtime. Each instance of Otto has a self-contained namespace.

func New Uses

func New() *Otto

New will allocate a new JavaScript runtime

func (Otto) Call Uses

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 (*Otto) Compile Uses

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 (*Otto) CompileWithSourceMap Uses

func (self *Otto) CompileWithSourceMap(filename string, src, sm interface{}) (*Script, error)

CompileWithSourceMap does the same thing as Compile, but with the obvious difference of applying a source map.

func (Otto) Context Uses

func (self Otto) Context() Context

Context returns the current execution context of the vm, traversing up to ten stack frames, and skipping any innermost native function stack frames.

func (Otto) ContextLimit Uses

func (self Otto) ContextLimit(limit int) Context

ContextLimit returns the current execution context of the vm, with a specific limit on the number of stack frames to traverse, skipping any innermost native function stack frames.

func (Otto) ContextSkip Uses

func (self Otto) ContextSkip(limit int, skipNative bool) (ctx Context)

ContextSkip returns the current execution context of the vm, with a specific limit on the number of stack frames to traverse, optionally skipping any innermost native function stack frames.

func (*Otto) Copy Uses

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 (Otto) Eval Uses

func (self Otto) Eval(src interface{}) (Value, error)

Eval will do the same thing as Run, except without leaving the current scope.

By staying in the same scope, the code evaluated has access to everything already defined in the current stack frame. This is most useful in, for example, a debugger call.

func (Otto) Get Uses

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 (Otto) MakeCustomError Uses

func (self Otto) MakeCustomError(name, message string) Value

MakeCustomError creates a new Error object with the given name and message, returning it as a Value.

func (Otto) MakeRangeError Uses

func (self Otto) MakeRangeError(message string) Value

MakeRangeError creates a new RangeError object with the given message, returning it as a Value.

func (Otto) MakeSyntaxError Uses

func (self Otto) MakeSyntaxError(message string) Value

MakeSyntaxError creates a new SyntaxError object with the given message, returning it as a Value.

func (Otto) MakeTypeError Uses

func (self Otto) MakeTypeError(message string) Value

MakeTypeError creates a new TypeError object with the given message, returning it as a Value.

func (Otto) Object Uses

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 (Otto) Run Uses

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 (Otto) Set Uses

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 (Otto) SetDebuggerHandler Uses

func (self Otto) SetDebuggerHandler(fn func(vm *Otto))

func (Otto) SetRandomSource Uses

func (self Otto) SetRandomSource(fn func() float64)

func (Otto) SetStackDepthLimit Uses

func (self Otto) SetStackDepthLimit(limit int)

SetStackDepthLimit sets an upper limit to the depth of the JavaScript stack. In simpler terms, this limits the number of "nested" function calls you can make in a particular interpreter instance.

Note that this doesn't take into account the Go stack depth. If your JavaScript makes a call to a Go function, otto won't keep track of what happens outside the interpreter. So if your Go function is infinitely recursive, you're still in trouble.

func (Otto) SetStackTraceLimit Uses

func (self Otto) SetStackTraceLimit(limit int)

SetStackTraceLimit sets an upper limit to the number of stack frames that otto will use when formatting an error's stack trace. By default, the limit is 10. This is consistent with V8 and SpiderMonkey.

TODO: expose via `Error.stackTraceLimit`

func (Otto) ToValue Uses

func (self Otto) ToValue(value interface{}) (Value, error)

ToValue will convert an interface{} value to a value digestible by otto/JavaScript.

type Script Uses

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

Script is a handle for some (reusable) JavaScript. Passing a Script value to a run method will evaluate the JavaScript.

func (*Script) String Uses

func (self *Script) String() string

type Value Uses

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

Value is the representation of a JavaScript value.

func FalseValue Uses

func FalseValue() Value

FalseValue will return a value representing false.

It is equivalent to:

ToValue(false)

func NaNValue Uses

func NaNValue() Value

NaNValue will return a value representing NaN.

It is equivalent to:

ToValue(math.NaN())

func NullValue Uses

func NullValue() Value

NullValue will return a Value representing null.

func ToValue Uses

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 Uses

func TrueValue() Value

TrueValue will return a value representing true.

It is equivalent to:

ToValue(true)

func UndefinedValue Uses

func UndefinedValue() Value

UndefinedValue will return a Value representing undefined.

func (Value) Call Uses

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:

1. There is an error during conversion of the argument list
2. The value is not actually a function
3. An (uncaught) exception is thrown

func (Value) Class Uses

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 (Value) Export Uses

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) IsBoolean Uses

func (value Value) IsBoolean() bool

IsBoolean will return true if value is a boolean (primitive).

func (Value) IsDefined Uses

func (value Value) IsDefined() bool

IsDefined will return false if the value is undefined, and true otherwise.

func (Value) IsFunction Uses

func (value Value) IsFunction() bool

IsFunction will return true if value is a function.

func (Value) IsNaN Uses

func (value Value) IsNaN() bool

IsNaN will return true if value is NaN (or would convert to NaN).

func (Value) IsNull Uses

func (value Value) IsNull() bool

IsNull will return true if the value is null, and false otherwise.

func (Value) IsNumber Uses

func (value Value) IsNumber() bool

IsNumber will return true if value is a number (primitive).

func (Value) IsObject Uses

func (value Value) IsObject() bool

IsObject will return true if value is an object.

func (Value) IsPrimitive Uses

func (value Value) IsPrimitive() bool

IsPrimitive will return true if value is a primitive (any kind of primitive).

func (Value) IsString Uses

func (value Value) IsString() bool

IsString will return true if value is a string (primitive).

func (Value) IsUndefined Uses

func (value Value) IsUndefined() bool

IsUndefined will return true if the value is undefined, and false otherwise.

func (Value) Object Uses

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) String Uses

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) ToBoolean Uses

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) ToFloat Uses

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) ToInteger Uses

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) ToString Uses

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.

Directories

PathSynopsis
astPackage ast declares types representing a JavaScript AST.
dbgPackage dbg is a println/printf/log-debugging utility library.
filePackage file encapsulates the file abstractions used by the ast & parser.
otto
parserPackage parser implements a parser for JavaScript.
registryPackage registry is an expirmental package to facillitate altering the otto runtime via import.
replPackage repl implements a REPL (read-eval-print loop) for otto.
terstPackage terst is a terse (terst = test + terse), easy-to-use testing library for Go.
test
tokenPackage token defines constants representing the lexical tokens of JavaScript (ECMA5).
underscorePackage underscore contains the source for the JavaScript utility-belt library.

Package otto imports 28 packages (graph) and is imported by 816 packages. Updated 2018-10-10. Refresh now. Tools for package owners.