Welcome!

Eclipse Authors: Liz McMillan, David H Deans, JP Morgenthal, Mano Marks, Yeshim Deniz

Related Topics: @CloudExpo, Java IoT, Containers Expo Blog, Eclipse

@CloudExpo: Blog Post

ES6 & Javascript in Harmony

An Overview of New Language Features

ES6 & Javascript in Harmony: An Overview of New Language Features

This article originally published on the Logentries blog.

ECMAScript 6 brings powerful new capabilities and some tasty syntactical sugar to the ubiquitous Javascript language, as it continues to grab an ever increasing slice of developer mindshare.

Now that the ES6 feature set is frozen and just minor refinements will be made over the coming months, much of this new functionality has already landed in modern browsers, and will continue to roll out with each new browser update.

For the impatient, there are also now several excellent precompile / polyfill / shim tools available, so you can start using these new features immediately; safely knowing that your code will run ‘natively' on every Javascript platform.

Javascript has become far more successful and ubiquitous than Brendan Eich or Netscape ever imagined, and several of the significant changes in the new spec, are designed with server side scripting platforms in mind (eg Node.js, and various scriptable database engines...).

This is an overview of some of the key changes in ES6

ES6 javascript new language features

Block Bindings

A new let keyword declares a variable (like var) but restricts its scope to the current code block (unlike var which is only scoped to function block); let also does not sharevar hoisting characteristics, so a let variable cannot be used until after its declaration (or it will throw an error).

function foo(){
  let x = 123;
  if(true){
    let x = 456;      
// different variable
    console.log(x);  
// 456
  }
  console.log(x);    
// 123
}

var i=0;
for(let i=i; i<10; i++){
  console.log(i);   
// 0 1 2 3 4 5 6 7 8 9
}
console.log(i)      
// 0

const is similar to let except once initialized, cannot be changed. const declarations share the same block scoping as let.

    const PI = 3.14159265359;
    let circumference = 2 * PI * r;

Arrow functions

Syntactical sugar (mostly) to facilitate simple function declaration, which is particularly handy for anonymous functions.

    // these are equivalent
    var sq = x => x * x
    var sq = function(x){ return x * x }

However, there are some important differences with standard function declarations:

  • The value of this inside an Arrow function is always determined by where it isdefinednot where it is used (avoiding common "var self = this" shuffle)
  • Arrow functions cannot change this within the function
  • Arrow functions cannot be used with new as constructors
  • Arrow functions have no arguments object, so must use standard named or new rest parameters
    var sum = (a,b) => a + b;
    var getName = () => "Pablo"; 
// empty parenthesis needed when no params
    var foo = (a,b) => { 
      let c = a + b; 
      console.log(a,b,c);        
// 1 2 3
    }

Because curly braces are used for the function's body, to return an object literal (outside of a function body) you must wrap the literal in parentheses.

var getObj = id => ({ id:id, name:"ObjA" });

Destructured assignment

Several variables can be initialized in a single statement and the following are equivalent:

    var [d, m, y] = [13, 2, 1963];
    var d = 13, m = 2, y = 1963;

    // useful for swapping
    [x, y] = [y, x]

    // or multiple return values
    function now(){ return [13, 2, 2013, 8, 0]; }
    var [d, m] = now(); // d = 13, m = 2
    var [,,y] = now(); // y = 2013

Destructuring also works with objects.

    function today() { return { d:13, m:2, y:1963 }; }
    var { m:month, y:year } = today(); 
// month = 2, year = 1963

// shorthand
    var { m, y } = today(); 
// m = 2, y = 1963

Destructuring assignments can also work with nested elements.

Parameters

There are several new conveniences for working with parameters.

Default Parameters

You can now assign default values to function parameters, which will be used if the parameter is not formally passed.

function myFunc( url, timeout=3000, callback=function(){} )

Rest Parameters

Designed to replace use of arguments when working with variable numbers of parameters, and indicated by three dots ... preceding a named parameter. The named parameter then becomes an array containing the rest of the parameters (passed but not specified).

    function sum(first, second, ...others){
      console.log(others.length);
    }

Spread Operator

Spread is the opposite of Rest parameters and splits an array into individual parameters.

    var a = [1,2,3,4,5]
    max = Math.max(...a) 
// equivalent to Math.max.apply(null,a) 
// or Math.max(1,2,3,4,5)

Spread can also be used in conjunction with other regular parameters.

Destructured Parameters

Similar to a destructured assignment (see above).

function setCookie( name, val, { secure, path, domain, expires })

Iterators and Generators

Iterators are objects that have a next() method which returns a results object with two properties, value and done. Iterators offer a collection of values one at a time through successive calls to next() returning the appropriate value or result with done==true if no more values to read.

ES6 collection objects (like arrays, maps and sets) all have three default iterators. These are entries()values() and keys() and cover most common iteration needs.

    var a=['one','two','three']
    for(let e of a.entries()) console.log(e)  
// [0,'one']  [1,'two']  [2,'three']
    for(let v of a.values()) console.log(v)   
// one  two  three
    for(let k of a.keys()) console.log(k)     
// 0  1  2

for..of

ES6 also introduces a new syntax for dealing with iterators. The for-of loop which is used for looping over iterable objects.

for(let i of ['one','two','three') console.log(i)

NOTE: for..of and for..in loops look similar, but are fundamentally different.for..in is for inspecting object properties and looping over the object's enumerable properties, whereas for..of is for looping over iterators.

for..of is also available in array comprehensions.

    [ x for (x of a) if (x>5) ]

Generators

A generator is a special kind of function that returns an iterator by inserting a * after thefunction keyword. A new yield keyword is used inside of generators to specify values that iterator should return when next() is called.

Generators stop execution after each yield until next() is called again, which is a powerful new paradigm (eg for managing asynchronous processes).

    function* gen(){
      yield 1;
      yield 2;
      yield 3;
    }
    let it = gen();
    for(let i of it) console.log(i); 
// outputs 1 2 3

    let it2 = gen();
    it2.next() // { value:0, done:false }
    it2.next() // { value:1, done:false }
    it2.next() // { value:2, done:false }
    it2.next() // { value:undefined, done:true }

Generators also let us write lazy versions of many functions (eg. filter, map, reduce...) which are very efficient and elegant.

Collections

ES6 introduces some new collection structures.

Sets

Sets are simple data structures similar to arrays where each value is unique.

    let s = new Set([1,2,3]);
    s.has(4);     // false
    s.add(4);     // [1,2,3,4]
    s.add(2);     // still [1,2,3,4]
    s.delete(3);  // [1,2,4]

Maps

Maps are similar to JavaScript object key-value pairs except the key can be any JavaScript data type, not just strings.

    m = new Map();
    o = {x:'blah'};
    m.set(o,'something to store');
    m.has(o); // true
    console.log(m.get(o));

Maps can also be used with iterators.

    for (let [k, v] of m) console.log(k, v);

Symbols

Symbols generate unique inaccessible keys, useful in maps and class private members.

    let a = Map();
    {
      let k = Symbol();
      a.set(k, 'value');
// Here, we can get and reset 'value' as a.get(k).
    }
// Here, a.get(k) is invalid, a.size is 1, 
// but the key cannot be seen.

WeakMaps and WeakSets

WeakMap helps developers avoid memory leaks by allowing the garbage collector to dispose objects only referenced by WeakMap. WeakMap keys must be objects and are not able to enumerate their keys.

WeakSet only objects, which can be collected if there are no other references or mentions.

Template Strings

New String declaration syntax (using back-ticks ") that facilitates simple String literals with embedded expression evaluation.

    var name = 'Paul', age = 99;
    var s = `$(name), is apparently $(age) years old`

The syntax can also be used fro simple multi-line strings.

    var longString = `here we have
     a multiline string 
     using backtick quotes`;

Promises

Promises are a mechanism for handling results (and errors) from asynchronous operations. You can achieve the same thing with callbacks, but promises provide improved readability via method chaining and simple error handling. Promises are already used in many JavaScript libraries.

    getJSON("/api/product/1").then( function(p) {
      return getJSON(p.description);
    }).catch(function(err) {
      console.log('Oops..',err)
    });

 

More Stories By Trevor Parsons

Trevor Parsons is Chief Scientist and Co-founder of Logentries. Trevor has over 10 years experience in enterprise software and, in particular, has specialized in developing enterprise monitoring and performance tools for distributed systems. He is also a research fellow at the Performance Engineering Lab Research Group and was formerly a Scientist at the IBM Center for Advanced Studies. Trevor holds a PhD from University College Dublin, Ireland.

@ThingsExpo Stories
Five years ago development was seen as a dead-end career, now it’s anything but – with an explosion in mobile and IoT initiatives increasing the demand for skilled engineers. But apart from having a ready supply of great coders, what constitutes true ‘DevOps Royalty’? It’ll be the ability to craft resilient architectures, supportability, security everywhere across the software lifecycle. In his keynote at @DevOpsSummit at 20th Cloud Expo, Jeffrey Scheaffer, GM and SVP, Continuous Delivery Busine...
SYS-CON Events announced today that Outscale, a global pure play Infrastructure as a Service provider and strategic partner of Dassault Systèmes, will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Founded in 2010, Outscale simplifies infrastructure complexities and boosts the business agility of its customers. Outscale delivers a secure, reliable and industrial strength solution for its customers, which in...
In order to meet the rapidly changing demands of today’s customers, companies are continually forced to redefine their business strategies in order to meet these needs, stay relevant and continue to see profitable growth. IoT deployment and development is integral in this transformation, and today businesses are increasingly seeing the value of investing their resources into IoT deployments. These technologies are able increase ROI through projects such as connecting supply chains or enabling sm...
SYS-CON Events announced today that CollabNet, a global leader in enterprise software development, release automation and DevOps solutions, will be a Bronze Sponsor of SYS-CON's 20th International Cloud Expo®, taking place from June 6-8, 2017, at the Javits Center in New York City, NY. CollabNet offers a broad range of solutions with the mission of helping modern organizations deliver quality software at speed. The company’s latest innovation, the DevOps Lifecycle Manager (DLM), supports Value S...
A strange thing is happening along the way to the Internet of Things, namely far too many devices to work with and manage. It has become clear that we'll need much higher efficiency user experiences that can allow us to more easily and scalably work with the thousands of devices that will soon be in each of our lives. Enter the conversational interface revolution, combining bots we can literally talk with, gesture to, and even direct with our thoughts, with embedded artificial intelligence, whic...
Everywhere we turn in our industry we can find strong opinions about the direction, type and nature of cloud’s impact on computing and business. Another word that is used in every context in our industry is “hybrid.” In his session at 20th Cloud Expo, Alvaro Gonzalez, Director of Technical, Partner and Field Marketing at Peak 10, will use a combination of a few conceptual props and some research recently commissioned by Peak 10 to offer a real-world consideration of how the various categories of...
SYS-CON Events announced today that Peak 10, Inc., a national IT infrastructure and cloud services provider, will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Peak 10 provides reliable, tailored data center and network services, cloud and managed services. Its solutions are designed to scale and adapt to customers’ changing business needs, enabling them to lower costs, improve performance and focus intern...
SYS-CON Events announced today that Super Micro Computer, Inc., a global leader in compute, storage and networking technologies, will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Supermicro (NASDAQ: SMCI), the leading innovator in high-performance, high-efficiency server technology, is a premier provider of advanced server Building Block Solutions® for Data Center, Cloud Computing, Enterprise IT, Hadoop/...
Multiple data types are pouring into IoT deployments. Data is coming in small packages as well as enormous files and data streams of many sizes. Widespread use of mobile devices adds to the total. In this power panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, panelists will look at the tools and environments that are being put to use in IoT deployments, as well as the team skills a modern enterprise IT shop needs to keep things running, get a handle on all this data, and deli...
SYS-CON Events announced today that SoftLayer, an IBM Company, has been named “Gold Sponsor” of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2016, at the Javits Center in New York, New York. SoftLayer, an IBM Company, provides cloud infrastructure as a service from a growing number of data centers and network points of presence around the world. SoftLayer’s customers range from Web startups to global enterprises.
In his opening keynote at 20th Cloud Expo, Michael Maximilien, Research Scientist, Architect, and Engineer at IBM, will motivate why realizing the full potential of the cloud and social data requires artificial intelligence. By mixing Cloud Foundry and the rich set of Watson services, IBM's Bluemix is the best cloud operating system for enterprises today, providing rapid development and deployment of applications that can take advantage of the rich catalog of Watson services to help drive insigh...
With major technology companies and startups seriously embracing Cloud strategies, now is the perfect time to attend @CloudExpo | @ThingsExpo, June 6-8, 2017, at the Javits Center in New York City, NY and October 31 - November 2, 2017, Santa Clara Convention Center, CA. Learn what is going on, contribute to the discussions, and ensure that your enterprise is on the right path to Digital Transformation.
SYS-CON Events announced today that EARP Integration will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. EARP Integration is a passionate software house. Since its inception in 2009 the company successfully delivers smart solutions for cities and factories that start their digital transformation. EARP provides bespoke solutions like, for example, advanced enterprise portals, business intelligence systems an...
SYS-CON Events announced today that Progress, a global leader in application development, has been named “Bronze Sponsor” of SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Enterprises today are rapidly adopting the cloud, while continuing to retain business-critical/sensitive data inside the firewall. This is creating two separate data silos – one inside the firewall and the other outside the firewall. Cloud ISVs oft...
As cloud adoption continues to transform business, today's global enterprises are challenged with managing a growing amount of information living outside of the data center. The rapid adoption of IoT and increasingly mobile workforce are exacerbating the problem. Ensuring secure data sharing and efficient backup poses capacity and bandwidth considerations as well as policy and regulatory compliance issues.
The 21st International Cloud Expo has announced that its Call for Papers is open. Cloud Expo, to be held October 31 - November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA, brings together Cloud Computing, Big Data, Internet of Things, DevOps, Digital Transformation, Machine Learning and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding busin...
Internet of @ThingsExpo, taking place October 31 - November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with the 21st International Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. @ThingsExpo Silicon Valley Call for Papers is now open.
SYS-CON Events announced today that Interoute has been named “Bronze Sponsor” of SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Interoute is the owner operator of Europe's largest network and a global cloud services platform, which encompasses over 70,000 km of lit fiber, 15 data centers, 17 virtual data centers and 33 colocation centers, with connections to 195 additional partner data centers. Our full-service Unifie...
DevOps is often described as a combination of technology and culture. Without both, DevOps isn't complete. However, applying the culture to outdated technology is a recipe for disaster; as response times grow and connections between teams are delayed by technology, the culture will die. A Nutanix Enterprise Cloud has many benefits that provide the needed base for a true DevOps paradigm.
SYS-CON Events announced today that Progress, a global leader in application development, has been named “Bronze Sponsor” of SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Enterprises today are rapidly adopting the cloud, while continuing to retain business-critical/sensitive data inside the firewall. This is creating two separate data silos – one inside the firewall and the other outside the firewall. Cloud ISVs ofte...