v8/test/mjsunit/harmony/arrow-functions.js

// Copyright 2014 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Flags: --harmony-arrow-functions

// Arrow functions are like functions, except they throw when using the
// "new" operator on them.
assertEquals("function", typeof (() => {}));
assertEquals(Function.prototype, Object.getPrototypeOf(() => {}));
assertThrows(function() { new (() => {}); }, TypeError);
assertFalse("prototype" in (() => {}));

// Check the different syntax variations
assertEquals(1, (() => 1)());
assertEquals(2, (a => a + 1)(1));
assertEquals(3, (() => { return 3; })());
assertEquals(4, (a => { return a + 3; })(1));
assertEquals(5, ((a, b) => a + b)(1, 4));
assertEquals(6, ((a, b) => { return a + b; })(1, 5));

// The following are tests from:
// http://wiki.ecmascript.org/doku.php?id=harmony:arrow_function_syntax

// Empty arrow function returns undefined
var empty = () => {};
assertEquals(undefined, empty());

// Single parameter case needs no parentheses around parameter list
var identity = x => x;
assertEquals(empty, identity(empty));

// No need for parentheses even for lower-precedence expression body
var square = x => x * x;
assertEquals(9, square(3));

// Parenthesize the body to return an object literal expression
var key_maker = val => ({key: val});
assertEquals(empty, key_maker(empty).key);

// Statement body needs braces, must use 'return' explicitly if not void
var evens = [0, 2, 4, 6, 8];
assertEquals([1, 3, 5, 7, 9], evens.map(v => v + 1));

var fives = [];
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10].forEach(v => {
  if (v % 5 === 0) fives.push(v);
});
assertEquals([5, 10], fives);