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Logical OR assignment:

Source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_OR_assignment

const a = { duration: 50, title: '' };

a.duration ||= 10;
console.log(a.duration);
// expected output: 50

a.title ||= 'title is empty.';
console.log(a.title);
// expected output: "title is empty"

Nullish coalescing operator

*Tip: This is different than Logical OR assignment.

Source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Nullish_coalescing_operator

const nullValue = null;
const emptyText = ""; // falsy
const someNumber = 42;

const valA = nullValue ?? "default for A";
const valB = emptyText ?? "default for B";
const valC = someNumber ?? 0;

console.log(valA); // "default for A"
console.log(valB); // "" (as the empty string is not null or undefined)
console.log(valC); // 42

Numeric separators

Source: https://v8.dev/features/numeric-separators

1_000_000_000_000
1_019_436_871.42

replace.all string method

Source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replaceAll

string.matchAll - amaz

Source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/matchAll

const regexp = /t(e)(st(\d?))/g;
const str = 'test1test2';

const array = [...str.matchAll(regexp)];

console.log(array[0]);
// expected output: Array ["test1", "e", "st1", "1"]

console.log(array[1]);
// expected output: Array ["test2", "e", "st2", "2"]

optional chaining

Source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Optional_chaining

const adventurer = {
  name: 'Alice',
  cat: {
    name: 'Dinah'
  }
};

const dogName = adventurer.dog?.name;
console.log(dogName);
// expected output: undefined

console.log(adventurer.someNonExistentMethod?.());
// expected output: undefined

top level await

Source: https://v8.dev/features/top-level-await

Source2: https://opensource.com/article/20/11/top-level-await-javascript#:~:text=Top%2Dlevel%20await%20is%20supported,has%20been%20added%20in%20Node.

await Promise.resolve(console.log('🎉'));
// → SyntaxError: await is only valid in async function

(async function() {
  await Promise.resolve(console.log('🎉'));
  // → 🎉
}());

In nodejs you can use (top-level await and ecma modules by doing it like:

// file: test.js
const asyncMsg = await Promise.resolve('WORKS')
console.log(asyncMsg)

and running command like below ways:

node --input-type=module --eval "$(cat test.js)"
cat test.js | node --input-type=module

//! Important:
node --input-type=module test.js
// THIS WOULD THROW ERROR AS CURRENTLY nodejs only allows `top-level await` and `esm modules`
// to be run via pipe operator or through command line argument i.e., eval flag only.

Better alternate is to use do:

• Change file exntension to .mjs instead of .js and then you can simply run like node test.mjs. LOVE.
• Specify "type": "module" in package.json file of the project.

array.at

Useful to get elements from back mostly, but you can use it to fetch elements using +ve index values directly as well.

Source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/at

array.at(1) // gives 2nd element as expected.
array.at(-1) // gives last element!
array.at(-2) // gives second last element!