diff --git a/js/.gitignore b/js/.gitignore
new file mode 100644
index 0000000..4e30131
--- /dev/null
+++ b/js/.gitignore
@@ -0,0 +1,6 @@
+/target
+**/*.rs.bk
+Cargo.lock
+bin/
+pkg/
+wasm-pack.log
diff --git a/js/Cargo.toml b/js/Cargo.toml
new file mode 100644
index 0000000..c7734ca
--- /dev/null
+++ b/js/Cargo.toml
@@ -0,0 +1,28 @@
+[package]
+name = "flatbush-wasm"
+version = "0.1.0"
+authors = ["Kyle Barron <kyle@developmentseed.org>"]
+edition = "2018"
+
+[lib]
+crate-type = ["cdylib", "rlib"]
+
+[features]
+default = ["console_error_panic_hook"]
+
+[dependencies]
+wasm-bindgen = "0.2.84"
+
+# The `console_error_panic_hook` crate provides better debugging of panics by
+# logging them with `console.error`. This is great for development, but requires
+# all the `std::fmt` and `std::panicking` infrastructure, so isn't great for
+# code size when deploying.
+console_error_panic_hook = { version = "0.1.7", optional = true }
+geo-index = { path = "../" }
+
+[dev-dependencies]
+wasm-bindgen-test = "0.3.34"
+
+[profile.release]
+# Tell `rustc` to optimize for small code size.
+opt-level = "s"
diff --git a/js/README.md b/js/README.md
new file mode 100644
index 0000000..3593e01
--- /dev/null
+++ b/js/README.md
@@ -0,0 +1,13 @@
+# WebAssembly bindings to geo-index
+
+Example WebAssembly bindings for the Rust [`geo-index`](https://github.com/kylebarron/geo-index) crate.
+
+This is not expected to be used _directly_ for JavaScript applications that only need an RTree or KDTree. In those cases, using [flatbush](https://github.com/mourner/flatbush) or [kdbush](https://github.com/mourner/kdbush) directly would probably give similar performance while being easier to use and smaller code size.
+
+However this is designed to show _how the underlying data can be used zero-copy_ between WebAssembly and JavaScript. A larger application could have some use for generating the RTree index in Rust in WebAssembly but then allowing JavaScript to view it and run queries on it.
+
+## Building
+
+```
+wasm-pack build --target web
+```
diff --git a/js/src/lib.rs b/js/src/lib.rs
new file mode 100644
index 0000000..22c6ace
--- /dev/null
+++ b/js/src/lib.rs
@@ -0,0 +1,20 @@
+mod rtree;
+mod utils;
+
+use wasm_bindgen::prelude::*;
+
+#[wasm_bindgen]
+extern "C" {
+    fn alert(s: &str);
+}
+
+#[wasm_bindgen]
+pub fn greet() {
+    alert("Hello, flatbush-wasm!");
+}
+
+/// Returns a handle to this wasm instance's `WebAssembly.Memory`
+#[wasm_bindgen(js_name = wasmMemory)]
+pub fn memory() -> JsValue {
+    wasm_bindgen::memory()
+}
diff --git a/js/src/rtree.rs b/js/src/rtree.rs
new file mode 100644
index 0000000..d13f463
--- /dev/null
+++ b/js/src/rtree.rs
@@ -0,0 +1,73 @@
+use geo_index::rtree::sort::HilbertSort;
+use geo_index::rtree::{RTree, RTreeBuilder};
+use wasm_bindgen::prelude::*;
+
+#[wasm_bindgen]
+pub struct FlatbushBuilder(RTreeBuilder<f64>);
+
+#[wasm_bindgen]
+impl FlatbushBuilder {
+    /// Construct a new FlatbushBuilder with number of items and node size
+    #[wasm_bindgen(constructor)]
+    pub fn new(num_items: u32, node_size: Option<u16>) -> Self {
+        let builder = if let Some(node_size) = node_size {
+            RTreeBuilder::new_with_node_size(num_items, node_size)
+        } else {
+            RTreeBuilder::new(num_items)
+        };
+        Self(builder)
+    }
+
+    /// Add a single box at a time to the builder
+    ///
+    /// This is less efficient than vectorized APIs.
+    pub fn add_single_box(&mut self, min_x: f64, min_y: f64, max_x: f64, max_y: f64) -> u32 {
+        self.0.add(min_x, min_y, max_x, max_y)
+    }
+
+    /// Add arrays of min_x, min_y, max_x, max_y to the builder
+    ///
+    /// Each array must be a Float64Array of the same length.
+    pub fn add_separated(
+        &mut self,
+        min_x: &[f64],
+        min_y: &[f64],
+        max_x: &[f64],
+        max_y: &[f64],
+    ) -> Vec<u32> {
+        assert_eq!(min_x.len(), min_y.len());
+        assert_eq!(min_x.len(), max_x.len());
+        assert_eq!(min_x.len(), max_y.len());
+
+        let mut out = Vec::with_capacity(min_x.len());
+        for i in 0..min_x.len() {
+            out.push(self.0.add(min_x[i], min_y[i], max_x[i], max_y[i]));
+        }
+        out
+    }
+
+    /// Finish this builder, sorting the index.
+    ///
+    /// This will consume this instance and convert it to a [Flatbush].
+    pub fn finish(self) -> Flatbush {
+        Flatbush(self.0.finish::<HilbertSort>())
+    }
+}
+
+#[wasm_bindgen]
+pub struct Flatbush(RTree<f64>);
+
+#[wasm_bindgen]
+impl Flatbush {
+    /// The byte offset within WebAssembly memory where the Flatbush memory starts.
+    #[wasm_bindgen]
+    pub fn byte_offset(&self) -> *const u8 {
+        self.0.as_ref().as_ptr()
+    }
+
+    /// The number of bytes in Flatbush memory
+    #[wasm_bindgen]
+    pub fn byte_length(&self) -> usize {
+        self.0.as_ref().len()
+    }
+}
diff --git a/js/src/utils.rs b/js/src/utils.rs
new file mode 100644
index 0000000..b1d7929
--- /dev/null
+++ b/js/src/utils.rs
@@ -0,0 +1,10 @@
+pub fn set_panic_hook() {
+    // When the `console_error_panic_hook` feature is enabled, we can call the
+    // `set_panic_hook` function at least once during initialization, and then
+    // we will get better error messages if our code ever panics.
+    //
+    // For more details see
+    // https://github.com/rustwasm/console_error_panic_hook#readme
+    #[cfg(feature = "console_error_panic_hook")]
+    console_error_panic_hook::set_once();
+}