If you call std::time::Instant::now() on a WASM platform, it will panic. This crate provides a partial
replacement for std::time::Instant that works on WASM too. This defines the type instant::Instant which is:
wasm32-unknown-unknown or wasm32-unknown-asmjs
and you enabled either the stdweb or the wasm-bindgen feature. This emulation is based on the javascript performance.now() function.std::time::Instant otherwise.Note that even if the stdweb or wasm-bindgen feature is enabled, this crate will continue to rely on std::time::Instant
as long as you are not targeting wasm32. This allows for portable code that will work on both native and WASM platforms.
This crate also exports the function instant::now() which returns a representation of the current time as an f64, expressed in milliseconds, in a platform-agnostic way. instant::now() will either:
performance.now() when compiling for a WASM platform with the features stdweb or wasm-bindgen enabled, or using a custom javascript function.Note: The old feature, now, has been deprecated. instant::now() is always exported and the now feature flag no longer has any effect. It remains listed in Cargo.toml to avoid introducing breaking changes and may be removed in future versions.
instant for a native platform.Cargo.toml:
toml
[dependencies]
instant = "0.1"
main.rs:
rust
fn main() {
// Will be the same as `std::time::Instant`.
let now = instant::Instant::now();
}
instant for a WASM platform.This example shows the use of the stdweb feature. It would be similar with wasm-bindgen.
Cargo.toml:
toml
[dependencies]
instant = { version = "0.1", features = [ "stdweb" ] }
main.rs:
rust
fn main() {
// Will emulate `std::time::Instant` based on `performance.now()`.
let now = instant::Instant::now();
}
instant for a WASM platform where performance.now() is not available.This example shows the use of the inaccurate feature.
Cargo.toml:
toml
[dependencies]
instant = { version = "0.1", features = [ "wasm-bindgen", "inaccurate" ] }
main.rs:
rust
fn main() {
// Will emulate `std::time::Instant` based on `Date.now()`.
let now = instant::Instant::now();
}
instant for any platform enabling a feature transitively.Cargo.toml: ```toml [features] stdweb = [ "instant/stdweb" ] wasm-bindgen = [ "instant/wasm-bindgen" ]
[dependencies] instant = "0.1" ```
lib.rs:
rust
fn my_function() {
// Will select the proper implementation depending on the
// feature selected by the user.
let now = instant::Instant::now();
}
instant::now()Cargo.toml: ```toml [features] stdweb = [ "instant/stdweb" ] wasm-bindgen = [ "instant/wasm-bindgen" ]
[dependencies] instant = "0.1" ```
lib.rs:
rust
fn my_function() {
// Will select the proper implementation depending on the
// feature selected by the user.
let now_instant = instant::Instant::now();
let now_milliseconds = instant::now(); // In milliseconds.
}
now without stdweb or wasm-bindgen.Cargo.toml:
toml
[dependencies]
instant = "0.1"
lib.rs:
rust
fn my_function() {
// Will use the 'now' javascript implementation.
let now_instant = instant::Instant::now();
let now_milliseconds = instant::now(); // In milliseconds.
}
javascript WASM bindings file:
js
function now() {
return Date.now() / 1000.0;
}