Comparison between ECMA5 and ECMA6 features
JavaScript
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ECMAScript 6 Features

Arrows

Arrows are a function shorthand using the => syntax. They are syntactically similar to the related feature in C#, Java 8 and CoffeeScript. They support both expression and statement bodies. Unlike functions, arrows share the same lexical this as their surrounding code.

Classes

ES6 classes are a simple sugar over the prototype-based OO pattern. Having a single convenient declarative form makes class patterns easier to use, and encourages interoperability. Classes support prototype-based inheritance, super calls, instance and static methods and constructors.

Enhanced Object Literals

Object literals are extended to support setting the prototype at construction, shorthand for foo: foo assignments, defining methods and making super calls. Together, these also bring object literals and class declarations closer together, and let object-based design benefit from some of the same conveniences.

Template Strings

Template strings provide syntactic sugar for constructing strings. This is similar to string interpolation features in Perl, Python and more. Optionally, a tag can be added to allow the string construction to be customized, avoiding injection attacks or constructing higher level data structures from string contents.

Destructuring

Destructuring allows binding using pattern matching, with support for matching arrays and objects. Destructuring is fail-soft, similar to standard object lookup foo["bar"], producing undefined values when not found.

Default, Rest, Spread

Callee-evaluated default parameter values. Turn an array into consecutive arguments in a function call. Bind trailing parameters to an array. Rest replaces the need for arguments and addresses common cases more directly.

Let, Const

Block-scoped binding constructs. let is the new var. const is single-assignment. Static restrictions prevent use before assignment.

Iterators, For..Of

Iterator objects enable custom iteration like CLR IEnumerable or Java Iterable. Generalize for..in to custom iterator-based iteration with for..of. Don’t require realizing an array, enabling lazy design patterns like LINQ.

Generators

Generators simplify iterator-authoring using function* and yield. A function declared as function* returns a Generator instance. Generators are subtypes of iterators which include additional next and throw. These enable values to flow back into the generator, so yield is an expression form which returns a value (or throws).

Modules

Language-level support for modules for component definition. Codifies patterns from popular JavaScript module loaders (AMD, CommonJS). Runtime behaviour defined by a host-defined default loader. Implicitly async model – no code executes until requested modules are available and processed.

ECMAScript 7 Features

Array Comprehension

The array comprehension syntax is a JavaScript expression which allows you to quickly assemble a new array based on an existing one.