Add date to json

src/js.rs

@@ -376,6 +376,12 @@ extern {
 #[wasm_bindgen]
 extern {
     pub type Date;
+    
+    /// The toJSON() method returns a string representation of the Date object.
+    /// 
+    /// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/toJSON
+    #[wasm_bindgen(method, js_name = toJSON)]
+    pub fn to_json(this: &Date) -> JsString;
 
     /// The toLocaleDateString() method returns a string with a language sensitive
     /// representation of the date portion of this date. The new locales and options

tests/all/js_globals/Date.rs

@@ -2,6 +2,34 @@
 
 use super::project;
 
+#[test]
+fn to_json() {
+    project()
+        .file("src/lib.rs", r#"
+            #![feature(proc_macro, wasm_custom_section)]
+
+            extern crate wasm_bindgen;
+            use wasm_bindgen::prelude::*;
+            use wasm_bindgen::js::{Date, JsString};
+
+            #[wasm_bindgen]
+            pub fn to_json(this: &Date) -> JsString {
+                this.to_json()
+            }
+        "#)
+        .file("test.ts", r#"
+            import * as assert from "assert";
+            import * as wasm from "./out";
+
+            export function test() {
+                let date = new Date('August 19, 1975 23:15:30 UTC');
+
+                assert.equal(wasm.to_json(date), '1975-08-19T23:15:30.000Z');
+            }
+        "#)
+        .test()
+}
+
 #[test]
 fn to_locale_date_string() {
     project()