#194 - Implement an alternative seed source via js-sys crate for WASM random numbers.

Author: thebracket

bracket-random/Cargo.toml

@@ -26,6 +26,9 @@ lazy_static = { version = "1.4.0", optional = true }
 serde_crate = { version = "~1.0.110", features = ["derive"], optional = true, package = "serde" }
 rand = { version = "0.8.3", default-features = false }
 
+[target.wasm32-unknown-unknown.dependencies]
+js-sys = "0.3.47"
+
 [dev-dependencies]
 criterion = "0.3.4"
 serde_json = "~1.0"

bracket-random/src/random.rs

@@ -6,6 +6,12 @@ use rand_xorshift::XorShiftRng;
 #[cfg(feature = "serde")]
 use serde_crate::{Deserialize, Serialize};
 
+
+#[cfg(target_arch = "wasm32")]
+fn unix_now() -> f64 {
+    js_sys::Date::now()
+}
+
 #[derive(Clone)]
 #[cfg_attr(
     feature = "serde",
@@ -19,6 +25,7 @@ pub struct RandomNumberGenerator {
 impl RandomNumberGenerator {
     /// Creates a new RNG from a randomly generated seed
     #[allow(clippy::new_without_default)] // XorShiftRng doesn't have a Default, so we don't either
+    #[cfg(not(target_arch = "wasm32"))]
     pub fn new() -> RandomNumberGenerator {
         use std::time::{SystemTime, UNIX_EPOCH};
         let rng: XorShiftRng = SeedableRng::seed_from_u64(
@@ -30,6 +37,15 @@ impl RandomNumberGenerator {
         RandomNumberGenerator { rng }
     }
 
+    #[cfg(target_arch = "wasm32")]
+    #[allow(clippy::new_without_default)] // XorShiftRng doesn't have a Default, so we don't either
+    pub fn new() -> RandomNumberGenerator {
+        let rng: XorShiftRng = SeedableRng::seed_from_u64(
+            unix_now() as u64
+        );
+        RandomNumberGenerator { rng }
+    }
+
     /// Creates a new RNG from a specific seed
     pub fn seeded(seed: u64) -> RandomNumberGenerator {
         let rng: XorShiftRng = SeedableRng::seed_from_u64(seed);