otto

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README

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.
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:

Usage

var ErrVersion = errors.New("version mismatch")
type Error
type Error struct {
}

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

func (Error) Error
func (err Error) Error() string

Error returns a description of the error

TypeError: 'def' is not a function
func (Error) String
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
type FunctionCall struct {
	This         Value
	ArgumentList []Value
	Otto         *Otto
}

FunctionCall is an encapsulation of a JavaScript function call.

func (FunctionCall) Argument
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
type Object struct {
}

Object is the representation of a JavaScript object.

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

Get the value of the property with the given name.

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

Get the keys for the object

Equivalent to calling Object.keys on the object

func (Object) Set
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
func (self Object) Value() Value

Value will return self as a value.

type Otto
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
func New() *Otto

New will allocate a new JavaScript runtime

func Run
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 (Otto) Call
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
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) Copy
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) Get
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) Object
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
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
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) ToValue
func (self Otto) ToValue(value interface{}) (Value, error)

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

type Script
type Script struct {
}

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

func (*Script) String
func (self *Script) String() string
type Value
type Value struct {
}

Value is the representation of a JavaScript value.

func FalseValue
func FalseValue() Value

FalseValue will return a value representing false.

It is equivalent to:

ToValue(false)
func NaNValue
func NaNValue() Value

NaNValue will return a value representing NaN.

It is equivalent to:

ToValue(math.NaN())
func NullValue
func NullValue() Value

NullValue will return a Value representing null.

func ToValue
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
func TrueValue() Value

TrueValue will return a value representing true.

It is equivalent to:

ToValue(true)
func UndefinedValue
func UndefinedValue() Value

UndefinedValue will return a Value representing undefined.

func (Value) Call
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
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
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
func (value Value) IsBoolean() bool

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

func (Value) IsDefined
func (value Value) IsDefined() bool

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

func (Value) IsFunction
func (value Value) IsFunction() bool

IsFunction will return true if value is a function.

func (Value) IsNaN
func (value Value) IsNaN() bool

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

func (Value) IsNull
func (value Value) IsNull() bool

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

func (Value) IsNumber
func (value Value) IsNumber() bool

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

func (Value) IsObject
func (value Value) IsObject() bool

IsObject will return true if value is an object.

func (Value) IsPrimitive
func (value Value) IsPrimitive() bool

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

func (Value) IsString
func (value Value) IsString() bool

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

func (Value) IsUndefined
func (value Value) IsUndefined() bool

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

func (Value) Object
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
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
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
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
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
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.

-- godocdown http://github.com/robertkrimen/godocdown

Documentation

Overview

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.

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

Constants

This section is empty.

Variables

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

Functions

func Run 

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.

Types

type Error 

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

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

func (Error) Error 

func (err Error) Error() string

Error returns a description of the error 

TypeError: 'def' is not a function

func (Error) String 

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 

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 

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 

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

Object is the representation of a JavaScript object.

func (Object) Call 

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 

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 

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

Get the value of the property with the given name.

func (Object) Keys 

func (self Object) Keys() []string

Get the keys for the object

Equivalent to calling Object.keys on the object

func (Object) Set 

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 

func (self Object) Value() Value

Value will return self as a value.

type Otto 

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 

func New() *Otto

New will allocate a new JavaScript runtime

func (Otto) Call 

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 

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) Copy 

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) Get 

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) Object 

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 

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 

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) ToValue 

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

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

type Script 

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 

func (self *Script) String() string

type Value 

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

Value is the representation of a JavaScript value.

func FalseValue 

func FalseValue() Value

FalseValue will return a value representing false.

It is equivalent to: 

ToValue(false)

func NaNValue 

func NaNValue() Value

NaNValue will return a value representing NaN.

It is equivalent to: 

ToValue(math.NaN())

func NullValue 

func NullValue() Value

NullValue will return a Value representing null.

func ToValue 

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 

func TrueValue() Value

TrueValue will return a value representing true.

It is equivalent to: 

ToValue(true)

func UndefinedValue 

func UndefinedValue() Value

UndefinedValue will return a Value representing undefined.

func (Value) Call 

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 

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 

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 

func (value Value) IsBoolean() bool

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

func (Value) IsDefined 

func (value Value) IsDefined() bool

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

func (Value) IsFunction 

func (value Value) IsFunction() bool

IsFunction will return true if value is a function.

func (Value) IsNaN 

func (value Value) IsNaN() bool

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

func (Value) IsNull 

func (value Value) IsNull() bool

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

func (Value) IsNumber 

func (value Value) IsNumber() bool

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

func (Value) IsObject 

func (value Value) IsObject() bool

IsObject will return true if value is an object.

func (Value) IsPrimitive 

func (value Value) IsPrimitive() bool

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

func (Value) IsString 

func (value Value) IsString() bool

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

func (Value) IsUndefined 

func (value Value) IsUndefined() bool

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

func (Value) Object 

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 

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 

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 

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 

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 

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.

Source Files

View all Source files

Directories

Path Synopsis
Package ast declares types representing a JavaScript AST.
 Package ast declares types representing a JavaScript AST.
Package dbg is a println/printf/log-debugging utility library.
 Package dbg is a println/printf/log-debugging utility library.
Package file encapsulates the file abstractions used by the ast & parser.
 Package file encapsulates the file abstractions used by the ast & parser.
Package parser implements a parser for JavaScript.
 Package parser implements a parser for JavaScript.
Package registry is an expirmental package to facillitate altering the otto runtime via import.
 Package registry is an expirmental package to facillitate altering the otto runtime via import.
Package terst is a terse (terst = test + terse), easy-to-use testing library for Go.
 Package terst is a terse (terst = test + terse), easy-to-use testing library for Go.
Package token defines constants representing the lexical tokens of JavaScript (ECMA5).
 Package token defines constants representing the lexical tokens of JavaScript (ECMA5).
Package underscore contains the source for the JavaScript utility-belt library.
 Package underscore contains the source for the JavaScript utility-belt library.

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