Welcome!

@CloudExpo Authors: Kevin Benedict, Kevin Jackson, Liz McMillan, Elizabeth White, 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.

@CloudExpo Stories
DevOps at Cloud Expo, taking place October 31 - November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 21st Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to w...
SYS-CON Events announced today that Massive Networks will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Massive Networks mission is simple. To help your business operate seamlessly with fast, reliable, and secure internet and network solutions. Improve your customer's experience with outstanding connections to your cloud.
"We want to show that our solution is far less expensive with a much better total cost of ownership so we announced several key features. One is called geo-distributed erasure coding, another is support for KVM and we introduced a new capability called Multi-Part," explained Tim Desai, Senior Product Marketing Manager at Hitachi Data Systems, in this SYS-CON.tv interview at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.
FinTechs use the cloud to operate at the speed and scale of digital financial activity, but are often hindered by the complexity of managing security and compliance in the cloud. In his session at 20th Cloud Expo, Sesh Murthy, co-founder and CTO of Cloud Raxak, showed how proactive and automated cloud security enables FinTechs to leverage the cloud to achieve their business goals. Through business-driven cloud security, FinTechs can speed time-to-market, diminish risk and costs, maintain continu...
There is a huge demand for responsive, real-time mobile and web experiences, but current architectural patterns do not easily accommodate applications that respond to events in real time. Common solutions using message queues or HTTP long-polling quickly lead to resiliency, scalability and development velocity challenges. In his session at 21st Cloud Expo, Ryland Degnan, a Senior Software Engineer on the Netflix Edge Platform team, will discuss how by leveraging a reactive stream-based protocol,...
DX World EXPO, LLC., a Lighthouse Point, Florida-based startup trade show producer and the creator of "DXWorldEXPO® - Digital Transformation Conference & Expo" has announced its executive management team. The team is headed by Levent Selamoglu, who has been named CEO. "Now is the time for a truly global DX event, to bring together the leading minds from the technology world in a conversation about Digital Transformation," he said in making the announcement.
In his session at 20th Cloud Expo, Mike Johnston, an infrastructure engineer at Supergiant.io, discussed how to use Kubernetes to set up a SaaS infrastructure for your business. Mike Johnston is an infrastructure engineer at Supergiant.io with over 12 years of experience designing, deploying, and maintaining server and workstation infrastructure at all scales. He has experience with brick and mortar data centers as well as cloud providers like Digital Ocean, Amazon Web Services, and Rackspace. H...
Internet of @ThingsExpo, taking place October 31 - November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 21st Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago. All major researchers estimate there will be tens of billions devic...
"The Striim platform is a full end-to-end streaming integration and analytics platform that is middleware that covers a lot of different use cases," explained Steve Wilkes, Founder and CTO at Striim, in this SYS-CON.tv interview at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.
Everything run by electricity will eventually be connected to the Internet. Get ahead of the Internet of Things revolution and join Akvelon expert and IoT industry leader, Sergey Grebnov, in his session at @ThingsExpo, for an educational dive into the world of managing your home, workplace and all the devices they contain with the power of machine-based AI and intelligent Bot services for a completely streamlined experience.
With tough new regulations coming to Europe on data privacy in May 2018, Calligo will explain why in reality the effect is global and transforms how you consider critical data. EU GDPR fundamentally rewrites the rules for cloud, Big Data and IoT. In his session at 21st Cloud Expo, Adam Ryan, Vice President and General Manager EMEA at Calligo, will examine the regulations and provide insight on how it affects technology, challenges the established rules and will usher in new levels of diligence...
SYS-CON Events announced today that Calligo has been named “Bronze Sponsor” of SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Calligo is an innovative cloud service provider offering mid-sized companies the highest levels of data privacy. Calligo offers unparalleled application performance guarantees, commercial flexibility and a personalized support service from its globally located cloud platfor...
SYS-CON Events announced today that Calligo, an innovative cloud service provider offering mid-sized companies the highest levels of data privacy and security, has been named "Bronze Sponsor" of SYS-CON's 21st International Cloud Expo ®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Calligo offers unparalleled application performance guarantees, commercial flexibility and a personalised support service from its globally located cloud plat...
What sort of WebRTC based applications can we expect to see over the next year and beyond? One way to predict development trends is to see what sorts of applications startups are building. In his session at @ThingsExpo, Arin Sime, founder of WebRTC.ventures, discussed the current and likely future trends in WebRTC application development based on real requests for custom applications from real customers, as well as other public sources of information.
SYS-CON Events announced today that SkyScale will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. SkyScale is a world-class provider of cloud-based, ultra-fast multi-GPU hardware platforms for lease to customers desiring the fastest performance available as a service anywhere in the world. SkyScale builds, configures, and manages dedicated systems strategically located in maximum-securit...
21st International Cloud Expo, taking place October 31 - November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy. Me...
SYS-CON Events announced today that DXWorldExpo has been named “Global Sponsor” of SYS-CON's 21st International Cloud Expo, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Digital Transformation is the key issue driving the global enterprise IT business. Digital Transformation is most prominent among Global 2000 enterprises and government institutions.
SYS-CON Events announced today that Datera, that offers a radically new data management architecture, has been named "Exhibitor" of SYS-CON's 21st International Cloud Expo ®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Datera is transforming the traditional datacenter model through modern cloud simplicity. The technology industry is at another major inflection point. The rise of mobile, the Internet of Things, data storage and Big...
"With Digital Experience Monitoring what used to be a simple visit to a web page has exploded into app on phones, data from social media feeds, competitive benchmarking - these are all components that are only available because of some type of digital asset," explained Leo Vasiliou, Director of Web Performance Engineering at Catchpoint Systems, in this SYS-CON.tv interview at DevOps Summit at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.
"Outscale was founded in 2010, is based in France, is a strategic partner to Dassault Systémes and has done quite a bit of work with divisions of Dassault," explained Jackie Funk, Digital Marketing exec at Outscale, in this SYS-CON.tv interview at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.