Struct js::jsapi::Value

#[repr(C)]
pub struct Value {
    pub data: jsval_layout,
}

JS::Value is the interface for a single JavaScript Engine value. A few general notes on JS::Value:

• JS::Value has setX() and isX() members for X in

  { Int32, Double, String, Symbol, Boolean, Undefined, Null, Object, Magic }

  JS::Value also contains toX() for each of the non-singleton types.

• Magic is a singleton type whose payload contains either a JSWhyMagic "reason" for the magic value or a uint32_t value. By providing JSWhyMagic values when creating and checking for magic values, it is possible to assert, at runtime, that only magic values with the expected reason flow through a particular value. For example, if cx->exception has a magic value, the reason must be JS_GENERATOR_CLOSING.

• The JS::Value operations are preferred. The JSVAL_* operations remain for compatibility; they may be removed at some point. These operations mostly provide similar functionality. But there are a few key differences. One is that JS::Value gives null a separate type. Also, to help prevent mistakenly boxing a nullable JSObject* as an object, Value::setObject takes a JSObject&. (Conversely, Value::toObject returns a JSObject&.) A convenience member Value::setObjectOrNull is provided.

• JSVAL_VOID is the same as the singleton value of the Undefined type.

• Note that JS::Value is 8 bytes on 32 and 64-bit architectures. Thus, on 32-bit user code should avoid copying jsval/JS::Value as much as possible, preferring to pass by const Value&.

Fields

data: jsval_layout

Trait Implementations

impl Debug for Value

fn fmt(&self, __arg_0: &mut Formatter) -> Result

Formats the value using the given formatter.

impl Copy for Value

impl Clone for Value

fn clone(&self) -> Self

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl RootKind for Value

fn rootKind() -> RootKind

impl Default for Value

fn default() -> Value

Returns the "default value" for a type.

impl GCMethods for Value

unsafe fn initial() -> Value

unsafe fn post_barrier(v: *mut Value, prev: Value, next: Value)