feat(Map): add Map.new

src/js.rs

@@ -331,6 +331,13 @@ extern {
     /// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map/has
     #[wasm_bindgen(method)]
     pub fn has(this: &Map, key: &JsValue) -> bool;
+
+    /// The Map object holds key-value pairs. Any value (both objects and 
+    /// primitive values) maybe used as either a key or a value.
+    /// 
+    /// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map
+    #[wasm_bindgen(constructor)]
+    pub fn new() -> Map;
 }
 
 // Math

tests/all/js_globals/Map.rs

@@ -125,3 +125,31 @@ fn has() {
         "#)
         .test()
 }
+
+#[test]
+fn new() {
+    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 new_map() -> js::Map {
+                js::Map::new()
+            }
+        "#)
+        .file("test.ts", r#"
+            import * as assert from "assert";
+            import * as wasm from "./out";
+
+            export function test() {
+                const map = wasm.new_map();
+
+                assert.equal(map.size, 0);
+            }
+        "#)
+        .test()
+}