Here are key features introduced in ES10 (ECMAScript 2019) with detailed descriptions and examples:

1. Array.flat() and Array.flatMap():

• Array.flat(): Flattens nested arrays into a single, shallower array.

JavaScript

const nestedArray = [[1, 2], [3, 4]];
const flattened = nestedArray.flat(); // [1, 2, 3, 4]

• Array.flatMap(): Combines mapping and flattening in one operation.

JavaScript

const numbers = [1, 2, 3];
const doubled = numbers.flatMap(x => [x, x * 2]); // [1, 2, 2, 4, 3, 6]

2. Object.fromEntries():

• Creates an object from a list of key-value pairs (arrays).

JavaScript

const entries = [["name", "John"], ["age", 30]];
const person = Object.fromEntries(entries); // { name: "John", age: 30 }

3. String.trimStart() and String.trimEnd():

• Remove whitespace from the beginning or end of strings.

JavaScript

const str = "  Hello World!  ";
const trimmedStart = str.trimStart(); // "Hello World!  "
const trimmedEnd = str.trimEnd(); // "  Hello World!"

4. Symbol.description:

• Provides a human-readable description for Symbols, useful for debugging.

JavaScript

const mySymbol = Symbol("foo");
mySymbol.description = "My special symbol";
console.log(mySymbol.description); // "My special symbol"

5. Optional Catch Binding:

• Eliminates the need to define an unused error variable in catch blocks.

JavaScript

try {
  // ...
} catch {
  // Handle error without explicit error variable
}

6. JSON Superset:

• Supports parsing JSON with JavaScript-like syntax, including unquoted property names and trailing commas.

JavaScript

const parsed = JSON.parse('{ a: 1, b: 2, }'); // Valid JSON

7. BigInt Primitive:

• Represents arbitrarily large integers beyond the safe integer limit of JavaScript numbers.

JavaScript

const bigNumber = 9007199254740991n; // BigInt literal

8. Dynamic Import:

• Loads modules dynamically at runtime using import().

JavaScript

const module = await import('./myModule.js');

Note: These features continue JavaScript’s evolution, offering more concise syntax, enhanced array and object manipulation, error handling, and data representation capabilities.