implements Object.preventExtensions() binding (#364)

src/js.rs

@@ -790,6 +790,14 @@ extern "C" {
     #[wasm_bindgen(constructor)]
     pub fn new() -> Object;
 
+    /// The Object.preventExtensions() method prevents
+    /// new properties from ever being added to an object
+    /// (i.e. prevents future extensions to the object).
+    /// 
+    /// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/preventExtensions
+    #[wasm_bindgen(static_method_of = Object, js_name = preventExtensions)]
+    pub fn prevent_extensions(object: &Object);
+
     /// The propertyIsEnumerable() method returns a Boolean indicating
     /// whether the specified property is enumerable.
     ///

tests/all/js_globals/Object.rs

@@ -180,6 +180,39 @@ fn keys() {
         .test()
 }
 
+#[test]
+fn prevent_extensions() {
+    project()
+        .file("src/lib.rs", r#"
+            #![feature(proc_macro, wasm_custom_section)]
+
+            extern crate wasm_bindgen;
+            use wasm_bindgen::prelude::*;
+            use wasm_bindgen::js;
+
+            #[wasm_bindgen]
+            pub fn prevent_extensions(obj: &js::Object) {
+                js::Object::prevent_extensions(obj);
+            }
+        "#)
+        .file("test.ts", r#"
+            import * as assert from "assert";
+            import * as wasm from "./out";
+
+            export function test() {
+                const object = {};
+                wasm.prevent_extensions(object);
+
+                assert(!Object.isExtensible(object));
+                assert.throws(() => {
+                    'use strict';
+                    Object.defineProperty(object, 'foo', { value: 42 });
+                }, TypeError);
+            }
+        "#)
+        .test()
+}
+
 #[test]
 fn property_is_enumerable() {
     project()