es6features

ECMAScript 6 git.io/es6features Introduction ECMAScript 6, also known as ECMAScript 2015, is the latest version of the ECMAScript standard. ES6 is a significant update to the language, and the first update to the language since ES5 was standardized in 2009. Implementation of these features in major JavaScript engines is underway now. See the ES6 standard for full specification of the ECMAScript 6 language. ES6 includes the following new features: arrows classes enhanced object literals template strings destructuring default + rest + spread let + const iterators + for..of generators unicode modules module loaders map + set + weakmap + weakset proxies symbols subclassable built-ins promises math + number + string + array + object APIs binary and octal literals reflect api tail calls ECMAScript 6 Features Arrows Arrows are a function shorthand using the => syntax. They are syntactically similar to the related feature in C#, Java 8 and CoffeeScript. They support both statement block bodies as well as expression bodies which return the value of the expression. Unlike functions, arrows share the same lexical this as their surrounding code. // Expression bodies var odds = evens.map(v => v + 1); var nums = evens.map((v, i) => v + i); var pairs = evens.map(v => ({even: v, odd: v + 1})); // Statement bodies nums.forEach(v => { if (v % 5 === 0) fives.push(v); }); // Lexical this var bob = { _name: "Bob", _friends: [], printFriends() { this._friends.forEach(f => console.log(this._name + " knows " + f)); } } More info: MDN Arrow Functions Classes ES6 classes are a simple sugar over the prototype-based OO pattern. Having a single convenient declarative form makes class patterns easier to use, and encourages interoperability. Classes support prototype-based inheritance, super calls, instance and static methods and constructors. class SkinnedMesh extends THREE.Mesh { constructor(geometry, materials) { super(geometry, materials); this.idMatrix = SkinnedMesh.defaultMatrix(); this.bones = []; this.boneMatrices = []; //... } update(camera) { //... super.update(); } get boneCount() { return this.bones.length; } set matrixType(matrixType) { this.idMatrix = SkinnedMesh[matrixType](); } static defaultMatrix() { return new THREE.Matrix4(); } } More info: MDN Classes Enhanced Object Literals Object literals are extended to support setting the prototype at construction, shorthand for foo: foo assignments, defining methods, making super calls, and computing property names with expressions. Together, these also bring object literals and class declarations closer together, and let object-based design benefit from some of the same conveniences. var obj = { // __proto__ __proto__: theProtoObj, // Shorthand for ‘handler: handler’ handler, // Methods toString() { // Super calls return "d " + super.toString(); }, // Computed (dynamic) property names [ 'prop_' + (() => 42)() ]: 42 }; More info: MDN Grammar and types: Object literals Template Strings Template strings provide syntactic sugar for constructing strings. This is similar to string interpolation features in Perl, Python and more. Optionally, a tag can be added to allow the string construction to be customized, avoiding injection attacks or constructing higher level data structures from string contents. // Basic literal string creation `In JavaScript '\n' is a line-feed.` // Multiline strings `In JavaScript this is not legal.` // String interpolation var name = "Bob", time = "today"; `Hello ${name}, how are you ${time}?` // Construct an HTTP request prefix is used to interpret the replacements and construction POST`http://foo.org/bar?a=${a}&b=${b} Content-Type: application/json X-Credentials: ${credentials} { "foo": ${foo}, "bar": ${bar}}`(myOnReadyStateChangeHandler); More info: MDN Template Strings Destructuring Destructuring allows binding using pattern matching, with support for matching arrays and objects. Destructuring is fail-soft, similar to standard object lookup foo["bar"], producing undefined values when not found. // list matching var [a, , b] = [1,2,3]; // object matching var { op: a, lhs: { op: b }, rhs: c } = getASTNode() // object matching shorthand // binds `op`, `lhs` and `rhs` in scope var {op, lhs, rhs} = getASTNode() // Can be used in parameter position function g({name: x}) { console.log(x); } g({name: 5}) // Fail-soft destructuring var [a] = []; a === undefined; // Fail-soft destructuring with defaults var [a = 1] = []; a === 1; More info: MDN Destructuring assignment Default + Rest + Spread Callee-evaluated default parameter values. Turn an array into consecutive arguments in a function call. Bind trailing parameters to an array. Rest replaces the need for arguments and addresses common cases more directly. function f(x, y=12) { // y is 12 if not passed (or passed as undefined) return x + y; } f(3) == 15 function f(x, ...y) { // y is an Array return x * y.length; } f(3, "hello", true) == 6 function f(x, y, z) { return x + y + z; } // Pass each elem of array as argument f(...[1,2,3]) == 6 More MDN info: Default parameters, Rest parameters, Spread Operator Let + Const Block-scoped binding constructs. let is the new var. const is single-assignment. Static restrictions prevent use before assignment. function f() { { let x; { // okay, block scoped name const x = "sneaky"; // error, const x = "foo"; } // error, already declared in block let x = "inner"; } } More MDN info: let statement, const statement Iterators + For..Of Iterator objects enable custom iteration like CLR IEnumerable or Java Iterable. Generalize for..in to custom iterator-based iteration with for..of. Don’t require realizing an array, enabling lazy design patterns like LINQ. let fibonacci = { [Symbol.iterator]() { let pre = 0, cu