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[...'apple']

Output: ['a', 'p', 'p', 'l', 'e']

Explanation: A STRING is an iterable type, and in an ARRAY, the spread operator transfers each character of an iterable to one element. As a result, each character in a string becomes an Array element.

Object initialization: VARIABLES with the same name are frequently used to create object PROPERTIES. Consider the following scenario:

In ES6, there's no need for tedious repetition!

Parsing returned objects: Only one value can be returned by a function, but that value could be an object with hundreds of properties and/or methods. In ES5, you must first get the returned object and then extract values from it. Consider the following scenario:

This is MADE easier by ES6 destructuring, which ELIMINATES the need to keep the object as a variable:

Babel is an open-source JAVASCRIPT transpiler that converts ECMAScript 2015+ (ES6+) code into a backwards compatible version of JavaScript that can be run by previous JavaScript engines. Babel is a popular tool for exploiting the JavaScript programming language's latest CAPABILITIES. 

Babel plugins are used to convert SYNTAX that isn't widely supported into a version that is backwards compatible. Arrow functions, for example, which are defined in ES6, are translated to ORDINARY function declarations. It's also possible to translate non-standard JavaScript syntax, such as JSX. Babel may automatically inject core-js polyfills for support capabilities that aren't available in JavaScript environments. Static methods like Array.from and built-ins like Promise, for example, are only accessible in ES6+, but they can be utilised in previous contexts by using core-js.

Symbols are a new type of object that can be USED as distinct property names in objects. Using Symbols instead of strings allows separate modules to create properties that are not mutually exclusive. Symbols can also be KEPT private, preventing anyone who does not have direct access to the SYMBOL from accessing its properties.

Symbols are a brand-new kind of primitive. Symbols, like numbers, strings, and booleans, have a function that can be used to produce them. Symbols, unlike the other primitives, do not have a literal SYNTAX (similar to how strings have ") and can only be created using the Symbol constructor:

In truth, Symbols are only a little different means of attaching properties to an object; the well-known Symbols could easily be provided as standard methods, just like Object.prototype.has Own Property which APPEARS in anything that inherits from Object.

• for in: runs over an object's ENUMERABLE property names.
• for of: (new in ES6) takes an object-specific ITERATOR and loops through the data it generates.

Both the for..of and for..in commands ITERATE over lists, but the RESULTS they return are different: for..in returns a list of keys on the object being iterated, whereas for..of returns a list of values of the object's numeric attributes.

When an EVENT OCCURS on the DOM, it does not TAKE place completely on one element. The event bubbles up or goes to its parent, grandparents, and grandparent's parent until it reaches the window in the Bubbling PHASE, whereas the event starts out from window down to the element that prompted the event or the event target in the Capturing Phase.

There are three stages of event propagation:

• Capturing Phase - the event begins with the window and progresses through each element until it reaches the target element.
• Target Phase - The event has arrived at the target element.
• Bubbling Phase - The event bubbles up from the target element and then up EVERY element until it reaches the window.

The extend keyword is used to implement inheritance in the ES6 language. There was no idea of classes in prior VERSIONS of Javascript, but with the release of ES6, Pure OBJECT ORIENTED ELEMENTS were added to the language.

With the help of the import STATEMENT, the export statement comes into picture when one needs to export functions, objects, and variables to other JavaScript modules. There are two methods for exporting:

• Named Export: Named exports are useful when one has to export multiple values. The name of the imported module must match that of the exported module.

Example:

Output:

• Default Export: There is only one default export per module when it comes to default exports. A function, a class, an OBJECT, or ANYTHING else can be used as a default export. In default export, the naming of imports is fully autonomous, and we can choose any name we like.

Example:

Output:

• Using Named and Default Exports at the same time: In the same file, you can utilise both Named and Default exports. It means they'll both be imported into the same document.

Output:

Promises mainly possess three states as follows:

• Pending: This refers to the initial state of every promise. It INDICATES that the result has not yet been computed.
• Fulfilled: It refers to the completion of a task.
• Rejected: It indicates the failure that ARISES during computation.

The promise will be immutable once it has been fulfilled or rejected. A rejected FUNCTION and a resolve function are the two arguments passed into the Promise() constructor. It returns either the first or second parameter, DEPENDING on the asynchronous OPERATION.

 IIFE is a JavaScript FUNCTION that starts running as soon as it is defined. The Self-Executing Anonymous Function is ANOTHER name for it. It is divided into two major sections, which are as follows:

• The first part is a lexical scope (STATIC scope) anonymous function that is enclosed by the Grouping OPERATOR ().
• The IIFE, which is used by JavaScript, is created in the second part. The function will be directly INTERPRETED by the engine.

Output:

If no value or undefined is passed, we can use the default PARAMETERS to set default VALUES for NAMED parameters.

Output:

In ES6, one way to define a class is to use the Class expression. Class expressions, like function expressions, can be named or unnamed. If the class is named, the name is unique to the class body. Prototype-based inheritance is used in JavaScript classes.

The syntax of a class expression is similar to that of a class statement (declaration). Class expressions, on the other HAND, allow you to omit the class name (“binding identifier”), which is not possible with class statements. Additionally, unlike class declarations, class expressions allow you to redefine/re-declare classes WITHOUT causing any TYPE errors. It is not required to use the constructor property. The type of classes created with this keyword will always be "function."

The KEYWORD CLASS is used to create a class in ES6. We can use class expressions or class declarations to INCLUDE classes in our code. Only functions and constructors are allowed in a class definition. These components are collectively referred to as the class's DATA members.

Constructors in classes are responsible for ALLOCATING memory to the class's objects. A class's functions are in charge of performing actions on the objects.

Syntax: In ES5

Syntax: In ES6 (Using class keyword)

Developers have discovered that ES6 classes are really HANDY. The following are some of the most common applications of ES6 classes:

• The syntax of ES6 classes is simpler and less prone to ERRORS.
• When it comes to building up inheritance HIERARCHIES, ES6 is the ideal option because it combines new and old syntax, reducing errors and simplifying the process.
• ES6 classes prevent developers from making mistakes when using a new operator. If this proves to be an invalid object for the constructor, classes ELIMINATE this issue by having the constructor throw an exception.
• Classes can also be used to call a method from the prototype's version. With the new ES6 syntax, this version is SIGNIFICANTLY easier to use than previous versions.

Template literals are a brand-new feature in ES6. It makes producing multiline strings and performing string interpolation simple.

Template literals, also known as string literals, allow for embedded expressions.

Template literals were REFERRED to as template strings prior to ES6. The backtick (``) character is used to enclose template literals. The dollar SIGN and curly BRACKETS (${expression}) are used to denote placeholders in template literals. If we need to use an expression within the BACKTICKS, we can put it in the (${expression}) variable.

Output:

It's a NEW feature in ES6 that enhances the ability to manage ARGUMENTS. Indefinite arguments can be represented as an array using rest parameters. We can INVOKE a function with any number of parameters by UTILIZING the rest parameter.

Output:

Asynchronous programming is a concept found in JavaScript. The processes are run separately from the main thread in asynchronous programming. Promises are the most convenient approach to deal with asynchronous programming in ES6. DEPENDING on the outcome of the procedure, a promise can be refused or RESOLVED. Callbacks were used to COPE with asynchronous programming before promises were introduced in ES6.

However, it caused the problem of callback hell, which was ADDRESSED with the introduction of promises.

(A callback is a function that is performed after another function has completed. When working with events in JavaScript, callback is very useful. As an ARGUMENT to another function, we pass a function into another function.

When we use callbacks in our web applications, it's common for them to get nested. Excessive callback usage clogs up your web application and leads to callback hell.)

Destructuring was INTRODUCED in ES6 as a way to extract DATA from arrays and objects into a SINGLE variable. It is possible to extract smaller fragments from objects and arrays using this method. The following is an example.

Output:

The list of parameters is OBTAINED using the spread operator. Three dots (...) are used to represent it. The spread operator divides an iterable (such as an array or a string) into individual elements. It's mostly used in JavaScript to make shallow copies of JS. It improves the READABILITY of your code by making it more concise.

The spread operator can be used to join two ARRAYS together or to concatenate them.

Output:

This is a NEWLY introduced feature in ES6. The Generator function returns an object after GENERATING several values over time. We can iterate over this object and extract values from the function one by one. A generator function returns an iterable object when called. In ES6, we use the * sign for a generator function along with the new ‘yield' keyword.

Output:

The yielded value becomes the next value in the sequence each time yield is invoked. Also, generators compute their output values on demand, ALLOWING them to efficiently represent expensive to compute SEQUENCES or even infinite sequences.

One should not use ARROW FUNCTIONS in the following cases:

• Function Hoisting, Named Functions:

As arrow functions are anonymous, we cannot use them when we want function hoisting or when we want to use named functions.

• Object methods:

The value of b does not drop when you call a.func. It's because this isn't bound to anything and will inherit the value from its parent scope.

• Callback functions with DYNAMIC CONTEXT:

We'd get a TypeError if we clicked the button. This is due to the fact that this is not bound to the button, but rather to its parent scope.

• this/arguments:

Since arrow functions don’t have this/arguments of their own and they depend on their outer context, we cannot use them in cases where we need to use this/arguments in a function.

In ES6, arrow functions are introduced. The shorthand syntax for writing ES6 functions is arrow functions. The arrow function's DEFINITION consists of parameters, followed by an arrow (=>), and the function's body.

The 'fat arrow' function is another NAME for the Arrow function. We won't be able to employ them as constructors.

Few things to note:

• It reduces the size of the code.
• For a single-line function, the return statement is optional.
• Bind the context lexically.
• For a single-line statement, functional braces are not required.
• Doesn’t WORK with new

When declaring any variable in JavaScript, we used the var keyword. Var is a function scoped keyword. Within a function, we can access the variable. When we need to CREATE a new scope, we wrap the code in a function.

Both LET and const have block scope. If you use these keywords to declare a variable, it will only exist within the innermost block that surrounds them. If you declare a variable with let INSIDE a block (for EXAMPLE, if a condition or a for-loop), it can only be accessed within that block.

The variables declared with the let keyword are mutable, which means that their values can be changed. It's akin to the var keyword, but with the added BENEFIT of block scoping. The variables declared with the const keyword are block-scoped and immutable. When variables are declared with the const keyword, their value cannot be modified or reassigned.

The object-oriented features supported in ES6 are:

• Classes: We can create classes in ES6. The class function essentially builds a template from which we may later create objects. When a new INSTANCE of the class is created, the constructor method is invoked.
• Methods: Static methods can also be found in classes. A static method, unlike an object, is a function that is BOUND to the class. A static method can't be called from a class instance.
  Let's take a look at getters and setters for a moment. Encapsulation is a FUNDAMENTAL notion in OOP. Data (object properties) should not be directly accessed or UPDATED from outside the object, which is a crucial aspect of encapsulation. A getter (access) or a setter (modify) are particular methods we define in our class to access or edit a property.
• Inheritance: It is also possible for classes to inherit from one another. The parent is the class that is being inherited from, and the child is the class that is inheriting from the parent.
   

Some of the common ES6 features are:

• Supports CONSTANTS/immutable variables.
• Block SCOPE support for all variables, constants and functions.
• Introduction to arrow functions
• Handling EXTENDED parameter
• Default parameters
• Extended and TEMPLATE literals
• De-structuring assignment
• Promises
• Classes
• Modules
• Collections
• Supports Map/Set & Weak-map/Weak-Set
• Localization, meta-programming, internationalization