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:

• A struct emulating the behavior of std::time::Instant if you are targeting 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.
• A type alias for 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:

• Call performance.now() when compiling for a WASM platform with the features stdweb or wasm-bindgen enabled, or using a custom javascript function.
• Return the time elapsed since the Unix Epoch on native, non-WASM platforms.

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.

Cargo.toml:

[dependencies]
instant = "0.1"

main.rs:

fn main() {
    // Will be the same as `std::time::Instant`.
    let now = instant::Instant::now();
}

This example shows the use of the stdweb feature. It would be similar with wasm-bindgen.

Cargo.toml:

[dependencies]
instant = { version = "0.1", features = [ "stdweb" ] }

main.rs:

fn main() {
    // Will emulate `std::time::Instant` based on `performance.now()`.
    let now = instant::Instant::now();
}

This example shows the use of the inaccurate feature.

Cargo.toml:

[dependencies]
instant = { version = "0.1", features = [ "wasm-bindgen", "inaccurate" ] }

main.rs:

fn main() {
    // Will emulate `std::time::Instant` based on `Date.now()`.
    let now = instant::Instant::now();
}

Cargo.toml:

[features]
stdweb = [ "instant/stdweb" ]
wasm-bindgen = [ "instant/wasm-bindgen" ]

[dependencies]
instant = "0.1"

lib.rs:

fn my_function() {
    // Will select the proper implementation depending on the
    // feature selected by the user.
    let now = instant::Instant::now();
}

Cargo.toml:

[features]
stdweb = [ "instant/stdweb" ]
wasm-bindgen = [ "instant/wasm-bindgen" ]

[dependencies]
instant = "0.1"

lib.rs:

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.
}

Cargo.toml:

[dependencies]
instant = "0.1"

lib.rs:

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:

function now() {
	return Date.now() / 1000.0;
}