feat(Map/MapIterator): add Map.keys

src/js.rs

@@ -367,6 +367,13 @@ extern {
     /// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map/entries
     #[wasm_bindgen(method)]
     pub fn entries(this: &Map) -> MapIterator;
+
+    /// The keys() method returns a new Iterator object that contains the 
+    /// keys for each element in the Map object in insertion order.
+    ///
+    /// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map/keys
+    #[wasm_bindgen(method)]
+    pub fn keys(this: &Map) -> MapIterator;
 }
 
 // Math

tests/all/js_globals/MapIterator.rs

@@ -34,3 +34,35 @@ fn entries() {
         "#)
         .test()
 }
+
+#[test]
+fn keys() {
+    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 get_keys(this: &js::Map) -> js::MapIterator {
+                this.keys()
+            }
+        "#)
+        .file("test.ts", r#"
+            import * as assert from "assert";
+            import * as wasm from "./out";
+
+            export function test() {
+                const map = new Map();
+                const iterator = map.keys();
+                const wasmIterator = wasm.get_keys(map);
+                map.set('foo', 'bar');
+                map.set('bar', 'baz');
+
+                assert.equal(iterator.toString(), wasmIterator.toString());
+            }
+        "#)
+        .test()
+}