Add js_sys::global

Author: alexcrichton

crates/js-sys/src/lib.rs

@@ -23,6 +23,8 @@ extern crate wasm_bindgen;
 use std::mem;
 use std::fmt;
 
+use std::sync::atomic::{AtomicUsize, ATOMIC_USIZE_INIT, Ordering::SeqCst};
+use wasm_bindgen::JsCast;
 use wasm_bindgen::prelude::*;
 
 // When adding new imports:
@@ -4100,3 +4102,54 @@ extern {
     #[wasm_bindgen(method)]
     pub fn finally(this: &Promise, cb: &Closure<FnMut()>) -> Promise;
 }
+
+/// Returns a handle to the global scope object.
+///
+/// This allows access to the global properties and global names by accessing
+/// the `Object` returned.
+pub fn global() -> Object {
+    // Cached `Box<JsValue>`, if we've already executed this.
+    //
+    // 0 = not calculated
+    // n = Some(n) == Some(Box<JsValue>)
+    static GLOBAL: AtomicUsize = ATOMIC_USIZE_INIT;
+
+    match GLOBAL.load(SeqCst) {
+        0 => {}
+        n => return unsafe { (*(n as *const JsValue)).clone().unchecked_into() },
+    }
+
+    // Ok we don't have a cached value, let's load one!
+    //
+    // According to StackOverflow you can access the global object via:
+    //
+    //      const global = Function('return this')();
+    //
+    // I think that's because the manufactured function isn't in "strict" mode.
+    // It also turns out that non-strict functions will ignore `undefined`
+    // values for `this` when using the `apply` function.
+    //
+    // As a result we use the equivalent of this snippet to get a handle to the
+    // global object in a sort of roundabout way that should hopefully work in
+    // all contexts like ESM, node, browsers, etc.
+    let this = Function::new_no_args("return this")
+        .call0(&JsValue::undefined())
+        .ok();
+
+    // Note that we avoid `unwrap()` on `call0` to avoid code size bloat, we
+    // just handle the `Err` case as returning a different object.
+    debug_assert!(this.is_some());
+    let this = match this {
+        Some(this) => this,
+        None => return JsValue::undefined().unchecked_into(),
+    };
+
+    let ptr: *mut JsValue = Box::into_raw(Box::new(this.clone()));
+    match GLOBAL.compare_exchange(0, ptr as usize, SeqCst, SeqCst) {
+        // We stored out value, relinquishing ownership of `ptr`
+        Ok(_) => {}
+        // Another thread one, drop our value
+        Err(_) => unsafe { drop(Box::from_raw(ptr)) },
+    }
+    this.unchecked_into()
+}

crates/test/src/rt/detect.rs

@@ -1,7 +1,8 @@
 //! Runtime detection of whether we're in node.js or a browser.
 
 use wasm_bindgen::prelude::*;
-use js_sys::Function;
+use wasm_bindgen::JsCast;
+use js_sys;
 
 #[wasm_bindgen]
 extern {
@@ -13,49 +14,8 @@ extern {
 /// Returns whether it's likely we're executing in a browser environment, as
 /// opposed to node.js.
 pub fn is_browser() -> bool {
-    // This is a bit tricky to define. The basic crux of this is that we want to
-    // test if the `self` identifier is defined. That is defined in browsers
-    // (and web workers!) but not in Node. To that end you might expect:
-    //
-    //      #[wasm_bindgen]
-    //      extern {
-    //          #[wasm_bindgen(js_name = self)]
-    //          static SELF: JsValue;
-    //      }
-    //
-    //      *SELF != JsValue::undefined()
-    //
-    // this currently, however, throws a "not defined" error in JS because the
-    // generated function looks like `function() { return self; }` which throws
-    // an error in Node because `self` isn't defined.
-    //
-    // To work around this limitation we instead lookup the value of `self`
-    // through the `this` object, basically generating `this.self`.
-    //
-    // Unfortunately that's also hard to do! In ESM modes the top-level `this`
-    // object is undefined, meaning that we can't just generate a function that
-    // returns `this.self` as it'll throw "can't access field `self` of
-    // `undefined`" whenever ESMs are being used.
-    //
-    // So finally we reach the current implementation. According to
-    // StackOverflow you can access the global object via:
-    //
-    //      const global = Function('return this')();
-    //
-    // I think that's because the manufactured function isn't in "strict" mode.
-    // It also turns out that non-strict functions will ignore `undefined`
-    // values for `this` when using the `apply` function. Add it all up, and you
-    // get the below code:
-    //
-    // * Manufacture a function
-    // * Call `apply` where we specify `this` but the function ignores it
-    // * Once we have `this`, use a structural getter to get the value of `self`
-    // * Last but not least, test whether `self` is defined or not.
-    //
-    // Whew!
-    let this = Function::new_no_args("return this")
-        .call0(&JsValue::undefined())
-        .unwrap();
-    assert!(this != JsValue::undefined());
-    This::from(this).self_() != JsValue::undefined()
+    // Test whether we're in a browser by seeing if the `self` property is
+    // defined on the global object, which should in turn only be true in
+    // browsers.
+    js_sys::global().unchecked_into::<This>().self_() != JsValue::undefined()
 }

crates/web-sys/src/lib.rs

@@ -15,52 +15,14 @@
 
 extern crate wasm_bindgen;
 extern crate js_sys;
+
 use js_sys::Object;
 
 #[cfg(feature = "Window")]
 pub fn window() -> Option<Window> {
-    use std::sync::atomic::{AtomicUsize, ATOMIC_USIZE_INIT, Ordering::SeqCst};
-    use wasm_bindgen::{JsValue, JsCast};
-
-    // Cached `Box<JsValue>`, if we've already executed this.
-    //
-    // 0 = not calculated
-    // 1 = `None`
-    // n = Some(n) == Some(Box<JsValue>)
-    static WINDOW: AtomicUsize = ATOMIC_USIZE_INIT;
-
-    match WINDOW.load(SeqCst) {
-        0 => {}
-        1 => return None,
-        n => return unsafe { Some((*(n as *const JsValue)).clone().unchecked_into()) },
-    }
-
-    // Ok we don't have a cached value, let's load one! Manufacture a function
-    // to get access to the `this` context and see if it's an instance of
-    // `Window`.
-    //
-    // Note that we avoid `unwrap()` on `call0` to avoid code size bloat, we
-    // just handle the `Err` case as returning `None`.
-    let window = js_sys::Function::new_no_args("return this")
-        .call0(&JsValue::undefined())
-        .ok()
-        .and_then(|w| w.dyn_into::<Window>().ok());
-
-    match &window {
-        None => WINDOW.store(1, SeqCst),
-        Some(window) => {
-            let window: &JsValue = window.as_ref();
-            let ptr: *mut JsValue = Box::into_raw(Box::new(window.clone()));
-            match WINDOW.compare_exchange(0, ptr as usize, SeqCst, SeqCst) {
-                // We stored out value, relinquishing ownership of `ptr`
-                Ok(_) => {}
-                // Another thread one, drop our value
-                Err(_) => unsafe { drop(Box::from_raw(ptr)) },
-            }
-        }
-    }
+    use wasm_bindgen::JsCast;
 
-    window
+    js_sys::global().dyn_into::<Window>().ok()
 }
 
 include!(concat!(env!("OUT_DIR"), "/bindings.rs"));