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

// Create a new runtime
Otto := otto.New()
Otto.Run(`
	abc = 2 + 2
	console.log("The value of abc is " + abc)
	// The value of abc is 4
`)
value, err := Otto.Get("abc")
{
	// value is an int64 with a value of 4
	value, _ := value.ToInteger()
}
Otto.Set("def", 11)
Otto.Run(`
	console.log("The value of def is " + def)
	// The value of def is 11
`)
Otto.Set("xyzzy", "Nothing happens.")
Otto.Run(`
	console.log(xyzzy.length) // 16
`)
value, _ = Otto.Run("xyzzy.length")
{
	// value is an int64 with a value of 16
	value, _ := value.ToInteger()
}
value, err = Otto.Run("abcdefghijlmnopqrstuvwxyz.length")
if err != nil {
	// err = ReferenceError: abcdefghijlmnopqrstuvwxyz is not defined
	// If there is an error, then value.IsUndefined() is true
	...
}

Robert Krimen <[email protected]>

-- type FunctionCall struct { This Value

    ArgumentList []Value
}

FunctionCall is an enscapulation 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(this Value, argumentList ...interface{}) (Value, error) Call the object as a function with the given this value and argument list and return the result of invocation. It is essentially equivalent to:

self.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 object is not actually a function
3. An (uncaught) exception is thrown

-- 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) 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.

-- type Otto struct { } 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(source string) (*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).

-- 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 not existing), 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, _ := Otto.Object(`Number`)

Or, creating a new object:

object, _ := Otto.Object(`{ xyzzy: "Nothing happens." }`)

Or, creating and assigning an object:

object, _ := Otto.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(source string) (Value, error) Run will run the given source (parsing it first), returning the resulting value and error (if any)

If the runtime is unable to parse the source, then this function will return undefined and the parse error (nothing will be evaluated in this case).

-- 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 being read-only, or the ToValue conversion failing), then an error is returned.

If the top-level binding does not exist, it will be created.

-- type Value struct { } Value is the representation of a JavaScript value.

-- func FalseValue() Value FalseValue will return a value represting 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)

-- func TrueValue() Value TrueValue will return a value represting 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:

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 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 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.