Struct JsOption 

pub struct JsOption<T = JsValue> { /* private fields */ }

A nullable JS value of type T.

Unlike Option<T>, which is a Rust-side construct, JsOption<T> represents a JS value that may be T, null, or undefined, where the null status is not yet known in Rust. The value remains in JS until inspected via methods like is_empty, as_option, or into_option.

T must implement JsGeneric, meaning it is any type that can be represented as a JsValue (e.g., JsString, Number, Object, etc.). JsOption<T> itself implements JsGeneric, so it can be used in all generic positions that accept JS types.

Implementations

impl<T> JsOption<T>

pub fn new() -> Self

Creates an empty JsOption<T> representing null.

pub fn wrap(val: T) -> Self

Wraps a value in a JsOption<T>.

pub fn from_option(opt: Option<T>) -> Self

Creates a JsOption<T> from an Option<T>.

Returns JsOption::wrap(val) if Some(val), otherwise JsOption::new().

pub fn is_empty(&self) -> bool

Tests whether this JsOption<T> is empty (null or undefined).

pub fn as_option(&self) -> Option<T>

Converts this JsOption<T> to an Option<T> by cloning the inner value.

Returns None if the value is null or undefined, otherwise returns Some(T) with a clone of the contained value.

pub fn into_option(self) -> Option<T>

Converts this JsOption<T> into an Option<T>, consuming self.

Returns None if the value is null or undefined, otherwise returns Some(T) with the contained value.

pub fn unwrap(self) -> T

Returns the contained value, consuming self.

Panics

Panics if the value is null or undefined.

pub fn expect(self, msg: &str) -> T

Returns the contained value, consuming self.

Panics

Panics if the value is null or undefined, with a panic message including the passed message.

pub fn unwrap_or_default(self) -> T

where T: Default,

Returns the contained value or a default.

Returns the contained value if not null or undefined, otherwise returns the default value of T.

pub fn unwrap_or_else<F>(self, f: F) -> T

where F: FnOnce() -> T,

Returns the contained value or computes it from a closure.

Returns the contained value if not null or undefined, otherwise calls f and returns the result.

Methods from Deref<Target = JsValue>

pub const NULL: JsValue

pub const UNDEFINED: JsValue

pub const TRUE: JsValue

pub const FALSE: JsValue

pub fn as_f64(&self) -> Option<f64>

Returns the f64 value of this JS value if it’s an instance of a number.

If this JS value is not an instance of a number then this returns None.

pub fn is_string(&self) -> bool

Tests whether this JS value is a JS string.

pub fn as_string(&self) -> Option<String>

If this JS value is a string value, this function copies the JS string value into Wasm linear memory, encoded as UTF-8, and returns it as a Rust String.

To avoid the copying and re-encoding, consider the JsString::try_from() function from js-sys instead.

If this JS value is not an instance of a string or if it’s not valid utf-8 then this returns None.

UTF-16 vs UTF-8

JavaScript strings in general are encoded as UTF-16, but Rust strings are encoded as UTF-8. This can cause the Rust string to look a bit different than the JS string sometimes. For more details see the documentation about the str type which contains a few caveats about the encodings.

pub fn as_bool(&self) -> Option<bool>

Returns the bool value of this JS value if it’s an instance of a boolean.

If this JS value is not an instance of a boolean then this returns None.

pub fn is_null(&self) -> bool

Tests whether this JS value is null

pub fn is_undefined(&self) -> bool

Tests whether this JS value is undefined

pub fn is_null_or_undefined(&self) -> bool

Tests whether this JS value is null or undefined

pub fn is_symbol(&self) -> bool

Tests whether the type of this JS value is symbol

pub fn is_object(&self) -> bool

Tests whether typeof self == "object" && self !== null.

pub fn is_array(&self) -> bool

Tests whether this JS value is an instance of Array.

pub fn is_function(&self) -> bool

Tests whether the type of this JS value is function.

pub fn is_bigint(&self) -> bool

Tests whether the type of this JS value is bigint.

pub fn js_typeof(&self) -> JsValue

Applies the unary typeof JS operator on a JsValue.

MDN documentation

pub fn js_in(&self, obj: &JsValue) -> bool

Applies the binary in JS operator on the two JsValues.

MDN documentation

pub fn is_truthy(&self) -> bool

Tests whether the value is “truthy”.

pub fn is_falsy(&self) -> bool

Tests whether the value is “falsy”.

pub fn loose_eq(&self, other: &Self) -> bool

Compare two JsValues for equality, using the == operator in JS.

MDN documentation

pub fn bit_not(&self) -> JsValue

Applies the unary ~ JS operator on a JsValue.

MDN documentation

pub fn unsigned_shr(&self, rhs: &Self) -> u32

Applies the binary >>> JS operator on the two JsValues.

MDN documentation

pub fn checked_div(&self, rhs: &Self) -> Self

Applies the binary / JS operator on two JsValues, catching and returning any RangeError thrown.

MDN documentation

pub fn pow(&self, rhs: &Self) -> Self

Applies the binary ** JS operator on the two JsValues.

MDN documentation

pub fn lt(&self, other: &Self) -> bool

Applies the binary < JS operator on the two JsValues.

MDN documentation

pub fn le(&self, other: &Self) -> bool

Applies the binary <= JS operator on the two JsValues.

MDN documentation

pub fn ge(&self, other: &Self) -> bool

Applies the binary >= JS operator on the two JsValues.

MDN documentation

pub fn gt(&self, other: &Self) -> bool

Applies the binary > JS operator on the two JsValues.

MDN documentation

pub fn unchecked_into_f64(&self) -> f64

Applies the unary + JS operator on a JsValue. Can throw.

MDN documentation

Trait Implementations

impl<T> AsRef<JsOption<T>> for JsOption<T>

fn as_ref(&self) -> &JsOption<T>

Converts this type into a shared reference of the (usually inferred) input type.

impl<T> AsRef<JsValue> for JsOption<T>

fn as_ref(&self) -> &JsValue

Converts this type into a shared reference of the (usually inferred) input type.

impl<T: Clone> Clone for JsOption<T>

fn clone(&self) -> JsOption<T>

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<T: JsGeneric + Debug> Debug for JsOption<T>

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

Formats the value using the given formatter.

impl<T: JsGeneric> Default for JsOption<T>

fn default() -> Self

Returns the “default value” for a type.

impl<T> Deref for JsOption<T>

type Target = JsValue

The resulting type after dereferencing.

fn deref(&self) -> &JsValue

Dereferences the value.

impl<T: JsGeneric + Display> Display for JsOption<T>

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

Formats the value using the given formatter.

impl<T> ErasableGeneric for JsOption<T>

type Repr = JsValue

The singular concrete type that all generic variants can be transmuted on

impl<T> From<JsOption<T>> for JsValue

fn from(obj: JsOption<T>) -> JsValue

Converts to this type from the input type.

impl From<JsValue> for JsOption

fn from(obj: JsValue) -> Self

Converts to this type from the input type.

impl<T> FromWasmAbi for JsOption<T>

type Abi = <JsValue as FromWasmAbi>::Abi

The Wasm ABI type that this converts from when coming back out from the ABI boundary.

unsafe fn from_abi(js: Self::Abi) -> Self

Recover a Self from Self::Abi.

impl<'a, T> IntoWasmAbi for &'a JsOption<T>

type Abi = <&'a JsValue as IntoWasmAbi>::Abi

The Wasm ABI type that this converts into when crossing the ABI boundary.

fn into_abi(self) -> Self::Abi

Convert self into Self::Abi so that it can be sent across the wasm ABI boundary.

impl<T> IntoWasmAbi for JsOption<T>

type Abi = <JsValue as IntoWasmAbi>::Abi

The Wasm ABI type that this converts into when crossing the ABI boundary.

fn into_abi(self) -> Self::Abi

Convert self into Self::Abi so that it can be sent across the wasm ABI boundary.

impl<T> JsCast for JsOption<T>

fn instanceof(val: &JsValue) -> bool

Performs a dynamic instanceof check to see whether the JsValue provided is an instance of this type.

fn unchecked_from_js(val: JsValue) -> Self

Performs a zero-cost unchecked conversion from a JsValue into an instance of Self

fn unchecked_from_js_ref(val: &JsValue) -> &Self

Performs a zero-cost unchecked conversion from a &JsValue into an instance of &Self.

fn has_type<T>(&self) -> bool

where T: JsCast,

Test whether this JS value has a type T.

fn dyn_into<T>(self) -> Result<T, Self>

where T: JsCast,

Performs a dynamic cast (checked at runtime) of this value into the target type T.

fn dyn_ref<T>(&self) -> Option<&T>

where T: JsCast,

Performs a dynamic cast (checked at runtime) of this value into the target type T.

fn unchecked_into<T>(self) -> T

where T: JsCast,

Performs a zero-cost unchecked cast into the specified type.

fn unchecked_ref<T>(&self) -> &T

where T: JsCast,

Performs a zero-cost unchecked cast into a reference to the specified type.

fn is_instance_of<T>(&self) -> bool

where T: JsCast,

Test whether this JS value is an instance of the type T.

fn is_type_of(val: &JsValue) -> bool

Performs a dynamic check to see whether the JsValue provided is a value of this type.

impl<T> LongRefFromWasmAbi for JsOption<T>

type Abi = <JsValue as LongRefFromWasmAbi>::Abi

Same as RefFromWasmAbi::Abi

type Anchor = JsOption<T>

Same as RefFromWasmAbi::Anchor

unsafe fn long_ref_from_abi(js: Self::Abi) -> Self::Anchor

Same as RefFromWasmAbi::ref_from_abi

impl<T> OptionFromWasmAbi for JsOption<T>

fn is_none(abi: &Self::Abi) -> bool

Tests whether the argument is a “none” instance. If so it will be deserialized as None, and otherwise it will be passed to FromWasmAbi.

impl<'a, T> OptionIntoWasmAbi for &'a JsOption<T>

fn none() -> Self::Abi

Returns an ABI instance indicating “none”, which JS will interpret as the None branch of this option.

impl<T> OptionIntoWasmAbi for JsOption<T>

fn none() -> Self::Abi

Returns an ABI instance indicating “none”, which JS will interpret as the None branch of this option.

impl<T: PartialEq> PartialEq for JsOption<T>

fn eq(&self, other: &JsOption<T>) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T> Promising for JsOption<T>

type Resolution = JsOption<T>

The type that this value resolves to.

impl<T> RefFromWasmAbi for JsOption<T>

type Abi = <JsValue as RefFromWasmAbi>::Abi

The Wasm ABI type references to Self are recovered from.

type Anchor = ManuallyDrop<JsOption<T>>

The type that holds the reference to Self for the duration of the invocation of the function that has an &Self parameter. This is required to ensure that the lifetimes don’t persist beyond one function call, and so that they remain anonymous.

unsafe fn ref_from_abi(js: Self::Abi) -> Self::Anchor

Recover a Self::Anchor from Self::Abi.

impl<T> StructuralPartialEq for JsOption<T>

impl<T> UpcastFrom<()> for JsOption<T>

impl<T1, Target1> UpcastFrom<(T1,)> for JsOption<(Target1,)>

where Target1: JsGeneric + UpcastFrom<T1>, T1: JsGeneric,

impl<T1, T2, Target1, Target2> UpcastFrom<(T1, T2)> for JsOption<(Target1, Target2)>

where Target1: JsGeneric + UpcastFrom<T1>, Target2: JsGeneric + UpcastFrom<T2>, T1: JsGeneric, T2: JsGeneric,

impl<T1, T2, T3, Target1, Target2, Target3> UpcastFrom<(T1, T2, T3)> for JsOption<(Target1, Target2, Target3)>

where Target1: JsGeneric + UpcastFrom<T1>, Target2: JsGeneric + UpcastFrom<T2>, Target3: JsGeneric + UpcastFrom<T3>, T1: JsGeneric, T2: JsGeneric, T3: JsGeneric,

impl<T1, T2, T3, T4, Target1, Target2, Target3, Target4> UpcastFrom<(T1, T2, T3, T4)> for JsOption<(Target1, Target2, Target3, Target4)>

where Target1: JsGeneric + UpcastFrom<T1>, Target2: JsGeneric + UpcastFrom<T2>, Target3: JsGeneric + UpcastFrom<T3>, Target4: JsGeneric + UpcastFrom<T4>, T1: JsGeneric, T2: JsGeneric, T3: JsGeneric, T4: JsGeneric,

impl<T1, T2, T3, T4, T5, Target1, Target2, Target3, Target4, Target5> UpcastFrom<(T1, T2, T3, T4, T5)> for JsOption<(Target1, Target2, Target3, Target4, Target5)>

where Target1: JsGeneric + UpcastFrom<T1>, Target2: JsGeneric + UpcastFrom<T2>, Target3: JsGeneric + UpcastFrom<T3>, Target4: JsGeneric + UpcastFrom<T4>, Target5: JsGeneric + UpcastFrom<T5>, T1: JsGeneric, T2: JsGeneric, T3: JsGeneric, T4: JsGeneric, T5: JsGeneric,

impl<T1, T2, T3, T4, T5, T6, Target1, Target2, Target3, Target4, Target5, Target6> UpcastFrom<(T1, T2, T3, T4, T5, T6)> for JsOption<(Target1, Target2, Target3, Target4, Target5, Target6)>

where Target1: JsGeneric + UpcastFrom<T1>, Target2: JsGeneric + UpcastFrom<T2>, Target3: JsGeneric + UpcastFrom<T3>, Target4: JsGeneric + UpcastFrom<T4>, Target5: JsGeneric + UpcastFrom<T5>, Target6: JsGeneric + UpcastFrom<T6>, T1: JsGeneric, T2: JsGeneric, T3: JsGeneric, T4: JsGeneric, T5: JsGeneric, T6: JsGeneric,

impl<T1, T2, T3, T4, T5, T6, T7, Target1, Target2, Target3, Target4, Target5, Target6, Target7> UpcastFrom<(T1, T2, T3, T4, T5, T6, T7)> for JsOption<(Target1, Target2, Target3, Target4, Target5, Target6, Target7)>

where Target1: JsGeneric + UpcastFrom<T1>, Target2: JsGeneric + UpcastFrom<T2>, Target3: JsGeneric + UpcastFrom<T3>, Target4: JsGeneric + UpcastFrom<T4>, Target5: JsGeneric + UpcastFrom<T5>, Target6: JsGeneric + UpcastFrom<T6>, Target7: JsGeneric + UpcastFrom<T7>, T1: JsGeneric, T2: JsGeneric, T3: JsGeneric, T4: JsGeneric, T5: JsGeneric, T6: JsGeneric, T7: JsGeneric,

impl<T1, T2, T3, T4, T5, T6, T7, T8, Target1, Target2, Target3, Target4, Target5, Target6, Target7, Target8> UpcastFrom<(T1, T2, T3, T4, T5, T6, T7, T8)> for JsOption<(Target1, Target2, Target3, Target4, Target5, Target6, Target7, Target8)>

where Target1: JsGeneric + UpcastFrom<T1>, Target2: JsGeneric + UpcastFrom<T2>, Target3: JsGeneric + UpcastFrom<T3>, Target4: JsGeneric + UpcastFrom<T4>, Target5: JsGeneric + UpcastFrom<T5>, Target6: JsGeneric + UpcastFrom<T6>, Target7: JsGeneric + UpcastFrom<T7>, Target8: JsGeneric + UpcastFrom<T8>, T1: JsGeneric, T2: JsGeneric, T3: JsGeneric, T4: JsGeneric, T5: JsGeneric, T6: JsGeneric, T7: JsGeneric, T8: JsGeneric,

impl<T, Target> UpcastFrom<*const T> for JsOption<*const Target>

where Target: UpcastFrom<T>,

impl UpcastFrom<JsError> for JsOption<JsValue>

impl<T> UpcastFrom<JsOption<T>> for JsValue

impl<T, U> UpcastFrom<JsOption<U>> for JsOption<T>

where T: UpcastFrom<U>,

impl UpcastFrom<JsValue> for JsOption<JsValue>

impl<T> UpcastFrom<Null> for JsOption<T>

impl<T, Target> UpcastFrom<Option<T>> for JsOption<Option<Target>>

where Target: UpcastFrom<T>,

impl<T, E, TargetT, TargetE> UpcastFrom<Result<T, E>> for JsOption<Result<TargetT, TargetE>>

where TargetT: UpcastFrom<T>, TargetE: UpcastFrom<E>,

impl<T> UpcastFrom<Undefined> for JsOption<T>

impl UpcastFrom<bool> for JsOption<JsValue>

impl UpcastFrom<char> for JsOption<JsValue>

impl UpcastFrom<f32> for JsOption<JsValue>

impl UpcastFrom<f32> for JsOption<f64>

impl UpcastFrom<f64> for JsOption<JsValue>

impl UpcastFrom<i128> for JsOption<JsValue>

impl UpcastFrom<i16> for JsOption<JsValue>

impl UpcastFrom<i16> for JsOption<i128>

impl UpcastFrom<i16> for JsOption<i32>

impl UpcastFrom<i16> for JsOption<i64>

impl UpcastFrom<i32> for JsOption<JsValue>

impl UpcastFrom<i32> for JsOption<i128>

impl UpcastFrom<i32> for JsOption<i64>

impl UpcastFrom<i32> for JsOption<isize>

impl UpcastFrom<i64> for JsOption<JsValue>

impl UpcastFrom<i64> for JsOption<i128>

impl UpcastFrom<i8> for JsOption<JsValue>

impl UpcastFrom<i8> for JsOption<i128>

impl UpcastFrom<i8> for JsOption<i16>

impl UpcastFrom<i8> for JsOption<i32>

impl UpcastFrom<i8> for JsOption<i64>

impl UpcastFrom<isize> for JsOption<JsValue>

impl UpcastFrom<isize> for JsOption<i128>

impl UpcastFrom<isize> for JsOption<i64>

impl UpcastFrom<u128> for JsOption<JsValue>

impl UpcastFrom<u16> for JsOption<JsValue>

impl UpcastFrom<u16> for JsOption<u128>

impl UpcastFrom<u16> for JsOption<u32>

impl UpcastFrom<u16> for JsOption<u64>

impl UpcastFrom<u32> for JsOption<JsValue>

impl UpcastFrom<u32> for JsOption<u128>

impl UpcastFrom<u32> for JsOption<u64>

impl UpcastFrom<u32> for JsOption<usize>

impl UpcastFrom<u64> for JsOption<JsValue>

impl UpcastFrom<u64> for JsOption<u128>

impl UpcastFrom<u8> for JsOption<JsValue>

impl UpcastFrom<u8> for JsOption<u128>

impl UpcastFrom<u8> for JsOption<u16>

impl UpcastFrom<u8> for JsOption<u32>

impl UpcastFrom<u8> for JsOption<u64>

impl UpcastFrom<usize> for JsOption<JsValue>

impl UpcastFrom<usize> for JsOption<u128>

impl UpcastFrom<usize> for JsOption<u64>