The TC-39 committee that oversees the ECMAScript general has brought many new capabilities, some of which can be syntactic sugar, but numerous of which have propelled us into an entirely new era of JavaScript programming. using itself, the async/look ahead to function guarantees us a way out of what is known as Callback Hell, or the scenario we discover ourselves in when nesting callbacks inside callbacks. it's such a vital function that it must necessitate a broad rethinking of the prevailing callback-orientated paradigm in Node.js and the relaxation of the JavaScript surroundings.

query('SELECT * from DB', function (err, result) { 

    if (err) throw err; // handle errors 

    // operate on result 

});

This was an essential insight on Ryan Dahl's component and is what propelled Node.js's reputation. certain moves take a long term to run, inclusive of database queries, and should not be handled similar to operations that quick retrieve information from memory. because of the nature of the JavaScript language, Node.js needed to express this asynchronous coding construct unnaturally. The effects do not appear at the following line of code, however as an alternative appears inside this callback feature. further, mistakes must be treated unnaturally, inside that callback characteristic.  Follow us for more information about Nodejs with Java from Nodejs Certification 

The convention in Node.js is that the first parameter to a callback feature is an error indicator, and the following parameters are the consequences. that is a useful convention that you'll find throughout the Node.js landscape. but, it complicates operating with outcomes and mistakes due to the fact both land in an inconvenient place — that callback function. The herbal place for errors and effects to land is on the subsequent line(s) of code.

We descend in addition to callback hell with each layer of callback function nesting. The seventh layer of callback nesting is more complicated than the 6th layer of callback nesting. Why? If not anything else, it is that the special concerns for errors managing come to be ever extra complex as callbacks are nested more deeply.

var results = await query('SELECT * from DB');

Instead, ES2017 async functions return us to this very natural expression of programming intent. Results and errors land in the correct location while preserving the excellent event-driven asynchronous programming model that made Node.js great. We'll see later in the book how this works.

The TC-39 committee added many more new features to JavaScript, such as:

Improved syntax for Class declarations making object inheritance and getter/setter functions very natural.

A new module format that is standardized across browsers and Node.js.

New methods for strings, such as the template string notation.

New methods for collections and arrays — for example, operations for map/reduce/filter.

The const keyword to define variables that cannot be changed, and the let keyword to define variables whose scope is limited to the block in which they're declared, rather than hoisted to the front of the function.

New looping constructs, and an iteration protocol that works with those new loops.

A new kind of function, the arrow function, which is lighter weight meaningless memory and execution time impact

The Promise object represents a result that is promised to be delivered in the future. By themselves, Promises can mitigate the callback hell problem, and they form part of the basis for async functions.

Generator functions are an intriguing way to represent asynchronous iteration over a set of values. More importantly, they form the other half of the basis for async functions.

You may see the new JavaScript described as ES6 or ES2017. What's the preferred name to describe the version of JavaScript that is being used?

ES1 through ES5 marked various phases of JavaScript's development. ES5 was released in 2009 and is widely implemented in modern browsers. Starting with ES6, the TC-39 committee decided to change the naming convention because of their intention to add new language features every year. Therefore, the language version name now includes the year, hence ES2015 was released in 2015, ES2016 was released in 2016, and ES2017 was released in 2017.

Deploying ES2015/2016/2017/2018 JavaScript code

The pink elephant within the room is that, because of how JavaScript is brought to the world, we cannot simply start the usage of state-of-the-art ES2017 features. In frontend JavaScript, we're restrained with the aid of the reality that old browsers are nonetheless in use. internet Explorer model 6 has luckily been nearly completely retired, however, there are nonetheless plenty of vintage browsers mounted on older computers which might be nonetheless serving a valid position for his or her proprietors. old browsers suggest old JavaScript implementations, and if we need our code to paintings, we want it to be well-matched with vintage browsers.

the use of code rewriting equipment consisting of Babel, a number of the brand new features may be retrofitted to feature on a number of the older browsers. Frontend JavaScript programmers can adopt (some of) the brand new functions on the fee of an extra complicated build toolchain, and the risk of insects delivered through the code rewriting process. a few may desire to try this, while others will prefer to wait a while.

The Node.js international does not have this trouble. Node.js has unexpectedly adopted ES2015/2016/2017 functions as quickly as they have been carried out in the V8 engine. With Node.js eight, we can now use async capabilities as a native function, and a maximum of the ES2015/2016 capabilities have become available with Node.js version 6. the new module format is now supported in Node.js version 10.

In other words, whilst frontend JavaScript programmers can argue that they have to wait more than one year earlier than adopting ES2015/2016/2017 capabilities, Node.js programmers haven't any need to wait. we can use the new capabilities with no need for any code rewriting equipment.

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