diff --git a/Cargo.toml b/Cargo.toml
index e80568ca..25d7d002 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -16,6 +16,7 @@ zip = {version = "0.6.4 ", default-features = false, features = ["deflate"]}
 regex = "1.7.3"
 lazy_static = "1.4.0"
 polars-error= {version = "0.32.1", default-features = false, features = [], optional = true }
+js-sys = {version = "0.3.64", optional = true}
 
 [dev-dependencies]
 pretty_assertions = "1.3.0"
@@ -37,6 +38,9 @@ chrono = ["dep:chrono"]
 # easier to write.
 polars = ["dep:polars-error"]
 
+# `wasm`: todo.
+wasm = ["js-sys"]
+
 # `test-resave`: Developer only testing feature.
 test-resave = []
 
diff --git a/src/datetime.rs b/src/datetime.rs
index 9c7a4709..93b95978 100644
--- a/src/datetime.rs
+++ b/src/datetime.rs
@@ -6,6 +6,12 @@
 
 #![warn(missing_docs)]
 use regex::Regex;
+
+#[cfg(not(all(
+    feature = "wasm",
+    target_arch = "wasm32",
+    not(any(target_os = "emscripten", target_os = "wasi"))
+)))]
 use std::time::SystemTime;
 
 #[cfg(feature = "chrono")]
@@ -1175,11 +1181,32 @@ impl ExcelDateTime {
     // Get the current UTC time. This is used to set some Excel metadata
     // timestamps.
     pub(crate) fn utc_now() -> String {
+        let timestamp = Self::system_now();
+        Self::unix_time_to_rfc3339(timestamp)
+    }
+
+    // Get the current time from the system time.
+    #[cfg(not(all(
+        feature = "wasm",
+        target_arch = "wasm32",
+        not(any(target_os = "emscripten", target_os = "wasi"))
+    )))]
+    fn system_now() -> u64 {
         let timestamp = SystemTime::now()
             .duration_since(SystemTime::UNIX_EPOCH)
             .expect("SystemTime::now() is before Unix epoch");
+        timestamp.as_secs()
+    }
 
-        Self::unix_time_to_rfc3339(timestamp.as_secs())
+    // Get the current time on Wasm/JS systems.
+    #[cfg(all(
+        feature = "wasm",
+        target_arch = "wasm32",
+        not(any(target_os = "emscripten", target_os = "wasi"))
+    ))]
+    fn system_now() -> u64 {
+        let timestamp = js_sys::Date::now();
+        timestamp as u64
     }
 
     // Convert to UTC date in RFC 3339 format. This is used in custom
diff --git a/src/packager.rs b/src/packager.rs
index 39184381..c238210f 100644
--- a/src/packager.rs
+++ b/src/packager.rs
@@ -42,6 +42,8 @@
 
 use std::collections::HashSet;
 use std::io::{Seek, Write};
+
+#[cfg(not(feature = "wasm"))]
 use std::thread;
 
 use zip::write::FileOptions;
@@ -110,6 +112,7 @@ impl<W: Write + Seek + Send> Packager<W> {
         // Assemble, but don't write, the worksheet files in parallel. These are
         // generally the largest files and the threading can help performance if
         // there are multiple large worksheets.
+        #[cfg(not(feature = "wasm"))]
         thread::scope(|scope| {
             for worksheet in &mut workbook.worksheets {
                 scope.spawn(|| {
@@ -118,6 +121,12 @@ impl<W: Write + Seek + Send> Packager<W> {
             }
         });
 
+        #[cfg(feature = "wasm")]
+        // For wasm targets don't use threading.
+        for worksheet in &mut workbook.worksheets {
+            worksheet.assemble_xml_file();
+        }
+
         // Write the worksheet file and and associated rel files.
         for (index, worksheet) in workbook.worksheets.iter_mut().enumerate() {
             self.write_worksheet_file(worksheet, index + 1)?;