ECMAScript (ES6 to ES13) - Features & Explanations

This README file provides detailed updates and explanations for ECMAScript (JavaScript) versions 6 through 13. Each version brought powerful new syntax, methods, and paradigms to modern JavaScript development.

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🌀 ES6 (ECMAScript 2015)

Major Updates & Explanations:

• let and const: Block-scoped variable declarations replacing var.
• Arrow Functions (=>): Shorter syntax, lexical this binding.
• Template Literals: Use backticks (``) to embed variables using ${}.
• Destructuring: Extract values from arrays/objects.
• Default Parameters: Assign default values in function definitions.
• Rest/Spread Operator (...): Group/ungroup values.
• Enhanced Object Literals: Property shorthand, method definitions.
• Classes: Syntactic sugar over prototype-based inheritance.
• Modules: import/export syntax for modular JavaScript.
• Promises: Handle asynchronous operations with .then() and .catch().
• New Data Structures: Map, Set, WeakMap, WeakSet.
• Symbols: New primitive for unique identifiers.
• Iterators & Generators: Custom iteration logic with yield.
• for...of Loop: Iterate over iterable objects (e.g., arrays).

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⚙️ ES7 (ECMAScript 2016)

Updates & Explanations:

• Array.prototype.includes(): Checks if array includes a value.
• Exponentiation Operator (**): 2 ** 3 is equivalent to Math.pow(2, 3).

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⚙️ ES8 (ECMAScript 2017)

Updates & Explanations:

• async/await: Syntactic sugar over Promises for readable async code.
• Object.values() / Object.entries(): Convert object to arrays.
• padStart() / padEnd(): Pad strings to a certain length.
• Object.getOwnPropertyDescriptors(): Fetch all property descriptors.
• Trailing Commas in Functions: Avoid syntax errors during edits.

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⚙️ ES9 (ECMAScript 2018)

Updates & Explanations:

• Rest/Spread Properties for Objects: Copy and extract object properties.
• Asynchronous Iteration (for await...of): Iterate over async iterables.
• Promise.prototype.finally(): Run code after promise settles.
• RegExp Enhancements:
  • Lookbehind assertions: /(?<=prefix)word/
  • Named capture groups: /(?<year>\d{4})/
  • DotAll flag (/s): . matches newline characters

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⚙️ ES10 (ECMAScript 2019)

Updates & Explanations:

• Array.prototype.flat() / flatMap(): Flatten nested arrays.
• Object.fromEntries(): Convert key-value array to object.
• trimStart() / trimEnd(): Trim whitespace.
• Optional Catch Binding: catch {} without parameter.
• Symbol Description: Symbol('desc').description returns 'desc'.

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⚙️ ES11 (ECMAScript 2020)

Updates & Explanations:

• Optional Chaining (?.): Safe access to deeply nested properties.
• Nullish Coalescing (??): Default only when null or undefined.
• BigInt: Arbitrary-precision integers (12345678901234567890n).
• Promise.allSettled(): Wait for all promises regardless of result.
• globalThis: Universal global object across environments.
• Dynamic import(): Load modules dynamically.
• import.meta: Metadata about current module.
• matchAll(): Returns all regex matches with capturing groups.
• Ordered for-in: Property order guarantee.

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⚙️ ES12 (ECMAScript 2021)

Updates & Explanations:

• Logical Assignment Operators:
  • ||=: Assign if falsy
  • &&=: Assign if truthy
  • ??=: Assign if nullish
• Numeric Separators: Improve readability (e.g., 1_000_000).
• String.prototype.replaceAll(): Replace all occurrences.
• WeakRefs & Finalizers: Advanced memory management tools.
• Promise.any(): Resolves as soon as one promise fulfills.
• AggregateError: Errors from Promise.any().

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⚙️ ES13 (ECMAScript 2022)

Updates & Explanations:

• Top-Level await: Use await outside async functions in modules.
• Class Fields:
  • Public: name = 'value'
  • Private: #id = 123
• .at() Method: Access index like arr.at(-1).
• Object.hasOwn(): Safer alternative to hasOwnProperty().
• Error Cause: Pass underlying error to new error instance.
• RegExp Match Indices (/d): Returns match start/end positions.

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✅ Summary Table

ES Version	Year	Key Features
ES6	2015	Classes, Modules, Promises
ES7	2016	includes(), ** operator
ES8	2017	async/await, object methods
ES9	2018	Rest/spread objects, RegEx improvements
ES10	2019	flat(), fromEntries(), trimStart()
ES11	2020	Optional chaining, BigInt, allSettled()
ES12	2021	replaceAll(), logical assignment, Promise.any()
ES13	2022	Class fields, .at(), top-level await

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🔗 References

• MDN Web Docs
• ECMAScript Spec