Struct JsValue

pub struct JsValue(/* private fields */);

The type of any JavaScript value, i.e., the root of all types.

The JsValue type is a catch-all type that sits at the top of the JavaScript type hierarchy. All JavaScript values can be safely and statically upcast to JsValue; by contrast, a downcast of a JsValue to another type requires a runtime check. (For TypeScript programmers, this can be thought of as similar to TypeScript’s unknown type.)

The JsValue type can be useful for generic, dynamic, or otherwise hard-to-express API signatures, such as overloaded types:

// Takes a string and adds the specified padding to the left.
// If the padding is a string, it's added as-is.
// If the padding is a number, then that number of spaces is added.
fn pad_left(mut cx: FunctionContext) -> JsResult<JsString> {
    let string: Handle<JsString> = cx.argument(0)?;
    let padding: Handle<JsValue> = cx.argument(1)?;

    let padding: String = if let Ok(str) = padding.downcast::<JsString, _>(&mut cx) {
        str.value(&mut cx)
    } else if let Ok(num) = padding.downcast::<JsNumber, _>(&mut cx) {
        " ".repeat(num.value(&mut cx) as usize)
    } else {
        return cx.throw_type_error("expected string or number");
    };

    let new_value = padding + &string.value(&mut cx);
    Ok(cx.string(&new_value))
}

Trait Implementations

impl Debug for JsValue

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Value for JsValue

fn to_string<'cx, C: Context<'cx>>(&self, cx: &mut C) -> JsResult<'cx, JsString>

fn as_value<'cx, C: Context<'cx>>(&self, _: &mut C) -> Handle<'cx, JsValue>

fn to_raw(&self) -> Value

Available on crate feature sys only.

Get a raw reference to the wrapped Node-API value.

unsafe fn from_raw<'cx, C: Context<'cx>>( cx: &C, value: Value, ) -> Handle<'cx, Self>

Available on crate feature sys only.

Creates a value from a raw Node-API value.