LibJS: Add support for arrow functions

Libraries/LibJS/Tests/arrow-functions.js

@@ -0,0 +1,57 @@
+function assert(x) { if (!x) throw 1; }
+try {
+  let getNumber = () => 42;
+  assert(getNumber() === 42);
+
+  let add = (a, b) => a + b;
+  assert(add(2, 3) === 5);
+
+  const addBlock = (a, b) => {
+    let res = a + b;
+    return res;
+  };
+  assert(addBlock(5, 4) === 9);
+
+  const makeObject = (a, b) => ({ a, b });
+  const obj = makeObject(33, 44);
+  assert(typeof obj === "object");
+  assert(obj.a === 33);
+  assert(obj.b === 44);
+
+  let returnUndefined = () => {};
+  assert(typeof returnUndefined() === "undefined");
+
+  const makeArray = (a, b) => [a, b];
+  const array = makeArray("3", { foo: 4 });
+  assert(array[0] === "3");
+  assert(array[1].foo === 4);
+
+  let square = x => x * x;
+  assert(square(3) === 9);
+
+  let squareBlock = x => {
+    return x * x;
+  };
+  assert(squareBlock(4) === 16);
+
+  const message = (who => "Hello " + who)("friends!");
+  assert(message === "Hello friends!");
+
+  const sum = ((x, y, z) => x + y + z)(1, 2, 3);
+  assert(sum === 6);
+
+  const product = ((x, y, z) => {
+    let res = x * y * z;
+    return res;
+  })(5, 4, 2);
+  assert(product === 40);
+
+  const half = (x => {
+    return x / 2;
+  })(10);
+  assert(half === 5);
+
+  console.log("PASS");
+} catch {
+  console.log("FAIL");
+}