HelsinkiJS meet-up. Dmitry Soshnikov - ECMAScript 6

@HelsinkiJS meet-up December 12, 2011 ECMAScript, 6 Dmitry Soshnikovhttp://dmitrysoshnikov.com

Function parameter default values

Function parameter default valuesfunction handleRequest(data, method) { method = method || “GET”; ...}

Function parameter default valuesfunction handleRequest(data, method) { method = method || “GET”; ...}function handleRequest(data, method = “GET”) { ...}

Modules system

Modules in ES3, ES5var DBLayer = (function (global) { /* save original */ var originalDBLayer = global.DBLayer; function noConflict() { global.DBLayer = originalDBLayer; 1. Create local scope } 2. Restoring function /* implementation */ 3. Implementation 4. Public API function query() { ... } /* exports, public API */ return { noConflict: noConflict, query: query };})(this);

Modules in ES3, ES5var DBLayer = (function (global) { /* save original */ var originalDBLayer = global.DBLayer; function noConflict() { global.DBLayer = originalDBLayer; 1. Create local scope } 2. Restoring function /* implementation */ 3. Implementation 4. Public API function query() { ... } /* exports, public API */ Too much of “noise”. return { A “sugar” is needed. noConflict: noConflict, query: query };})(this);

Modules in ES6module DBLayer { export function query(s) { ... } export function connection(...args) { ... }}import * from DBLayer; // import all// import only needed exportsimport {query, connection: attachTo} from DBLayerquery(“SELECT * FROM books”).format(“escape | split”);attachTo(“/books/store”, { onSuccess: function (response) { ... }})

Quasi-Literals(String templates)

Quasis : string templateslet content = “<a href=‘” + url + “’ title=‘” + title + “’>” + text+ “</a>”;$(“#bar”).html(content);

Quasis : string templateslet content = “<a href=‘” + url + “’ title=‘” + title + “’>” + text+ “</a>”;$(“#bar”).html(content);let content = safeHtml `<a href=“${url} “ title=“${title}”>${text}</a>`;$(“#bar”).html(content);See: http://wiki.ecmascript.org/doku.php?id=harmony:quasis

Array comprehensions

Array comprehensions// map + filter waylet scores = [1, 7, 4, 9] .filter(function (x) { return x > 5 }) .map(function (x) { return x * x }); // [49, 81]

Array comprehensions// map + filter waylet scores = [1, 7, 4, 9] .filter(function (x) { return x > 5 }) .map(function (x) { return x * x }); // [49, 81]// array comprehensionslet scores = [x * x for (x in values([1, 7, 4, 9])) if (x > 5)];

Map and WeakMap

Map and WeakMaplet user = {name: “Ann”, x: 10, y: 20};// Keys in a map are objectslet scoresMap = new Map;map.set(user, 100);console.log(scoresMap.get(user)); // 100

Map and WeakMaplet user = {name: “Ann”, x: 10, y: 20};// Keys in a map are objectslet scoresMap = new Map;map.set(user, 100);console.log(scoresMap.get(user)); // 100let markers = new WeakMap;marker = new Marker(10, 20);markers.set(marker, “Ann”);console.log(weakMap.get(marker)); // “Ann”delete marker; // if marker is GC’ed, it’s removed from WeakMap too!

Destructuring assignment

Destructuring: arrays// for arrayslet [x, y] = [10, 20, 30];console.log(x, y); // 10, 20

Destructuring of function parametersfunction Panel(config) { var title = config.title; var x = config.pos[0]; Too “noisy” var y = config.pos[1]; return title + x + y;}new Panel({title: “Users”, pos: [10, 15]});

Destructuring of function parametersfunction Panel({title: title, pos: [x, y]}) { return title + x + y;}let config = {title: “Users”, pos: [10, 15]};new Panel(config);

Eliminating of arguments: ...rest operator

Object arguments// ES3, ES5function format(pattern /*, rest */) { var rest = [].slice.call(arguments, 1); var items = rest.filter(function (x) { return x > 1}); return pattern.replace(“%v”, items);}format(“scores: %v”, 1, 5, 3); // scores: 5, 3

Complicated arguments// ES3, ES5function format(pattern /*, rest */) { var rest = [].slice.call(arguments, 1); // complicated var items = rest.filter(function (x) { return x > 1}); return pattern.replace(“%v”, items);}format(“scores: %v”, 1, 5, 3); // scores: 5, 3

...rest// ES6 aka Harmonyfunction format(pattern, …rest) { // real array var items = rest.filter(function (x) { return x > 1}); return pattern.replace(“%v”, items);}format(“scores: %v”, 1, 5, 3); // scores: 5, 3

Proxy objects : meta level

Proxy-objects/* target – original object * handler – meta-handler */Proxy(target, handler)See: http://wiki.ecmascript.org/doku.php?id=harmony:direct_proxiesNote: old semantics (currently is implemented in Firefox) will not longer be available:Proxy.create(handler, [proto]), Proxy.createFunction(handler, [call, [consruct]])See: http://wiki.ecmascript.org/doku.php?id=harmony:proxies

Proxy-objects // original object // proxied object let point = { let loggedPoint = Proxy(point, { x: 10, get: function (point, name, rcvr) { y: 20 console.log(“get: ”, name); }; return point[name]; }, set: function (point, name, value, rcvr) {Trap of getting of console.log(“set: ”, name, value); properties point[name] = value; }Trap of setting the }); properties

Proxy-objects // proxied object Meta-handler let loggedPoint = Proxy(point, { get: function (point, name, rcvr) {// reading trap console.log(“get: ”, name);loggedPoint.x; // get: x, 10 return point[name]; },// writing trap set: function (point, name, value, rcvr) {loggedPoint.x = 20; // set: x, 20 console.log(“set: ”, name, value); point[name] = value;// reflected on the original object }point.x; // 20 });

Struct types

Struct types// struct typeslet Point2D = new StructType({ x: uint32, y: uint32 });let Color = new StructType({ r: uint8, g: uint8, b: uint8 });let Pixel = new StructType({ point: Point2D, color: Color });// array typeslet Triangle = new ArrayType(Pixel, 3);// dense-objects, based on struct binary typeslet t = new Triangle([ { point: { x: 0, y: 0 }, color: { r: 255, g: 255, b: 255 } }, { point: { x: 5, y: 5 }, color: { r: 128, g: 0, b: 0 } }, { point: { x: 10, y: 0 }, color: { r: 0, g: 0, b: 128 } }]);

Struct types : example// struct typeslet IODataBlock = new StructType( /* attributes */ );stream.read(IODataBlock, function (block) { // partial handling});

Thanks for your attention Dmitry Soshnikovdmitry.soshnikov@gmail.com http://dmitrysoshnikov.com @DmitrySoshnikov

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HelsinkiJS meet-up. Dmitry Soshnikov - ECMAScript 6

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