feat(Map): add Map.has

src/js.rs

@@ -324,6 +324,13 @@ extern {
     /// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map/get
     #[wasm_bindgen(method)]
     pub fn get(this: &Map, key: &JsValue) -> JsValue;
+
+    /// The has() method returns a boolean indicating whether an element with 
+    /// the specified key exists or not.
+    /// 
+    /// 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;
 }
 
 // Math

tests/all/js_globals/Map.rs

@@ -96,3 +96,32 @@ fn get() {
         "#)
         .test()
 }
+
+#[test]
+fn has() {
+    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 has(this: &js::Map, key: &JsValue) -> bool {
+                this.has(key)
+            }
+        "#)
+        .file("test.ts", r#"
+            import * as assert from "assert";
+            import * as wasm from "./out";
+
+            export function test() {
+                const map = new Map();
+                map.set('foo', 'bar');
+                assert.equal(wasm.has(map, 'foo'), true);
+                assert.equal(wasm.has(map, 'bar'), false);
+            }
+        "#)
+        .test()
+}