add JsString binding to src/js.rs and tests

Author: kzvi

src/js.rs

@@ -255,3 +255,17 @@ extern {
     #[wasm_bindgen(method, js_name = propertyIsEnumerable)]
     pub fn property_is_enumerable(this: &Object, property: &JsValue) -> bool;
 }
+
+// String
+#[wasm_bindgen]
+extern {
+    #[wasm_bindgen(js_name = String)]
+    pub type JsString;
+
+    /// The slice() method extracts a section of a string and returns it as a
+    /// new string, without modifying the original string.
+    ///
+    /// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/slice
+    #[wasm_bindgen(method, js_class = "String")]
+    pub fn slice(this: &JsString, start: u32, end: u32) -> JsString;
+}

tests/all/js_globals/JsString.rs

@@ -0,0 +1,32 @@
+#![allow(non_snake_case)]
+
+use project;
+
+#[test]
+fn slice() {
+    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 create_slice(this: &js::JsString, start: u32, end: u32) -> js::JsString {
+                this.slice(start, end)
+            }
+        "#)
+        .file("test.ts", r#"
+            import * as assert from "assert";
+            import * as wasm from "./out";
+
+            export function test() {
+                let characters = "acxn18";
+                let subset = wasm.create_slice(characters, 1, 3);
+
+                assert.equal(subset, "cx");
+            }
+        "#)
+        .test()
+}

tests/all/js_globals/mod.rs

@@ -5,6 +5,7 @@ use super::project;
 mod Object;
 mod Array;
 mod ArrayIterator;
+mod JsString;
 
 #[test]
 #[cfg(feature = "std")]