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Node.js (v.15) 4 things to know.

 

The V8 JavaScript engine has been updated to V8 8.6 

(V8 8.4 is the latest available in Node.js 14). 

Along with performance tweaks and improvements the V8 update also brings 

the following language features:


1)Promise.any():


Promise.any() takes an iterable of Promise objects and, as soon as one of the promises in the iterable fulfills, 

returns a single promise that resolves with the value from that promise. 

If no promises in the iterable fulfill (if all of the given promises are rejected), 

then the returned promise is rejected with an AggregateError.



Example:

const promise1 = Promise.reject(0);

const promise2 = new Promise((resolve) => setTimeout(resolve, 100, 'quick'));

const promise3 = new Promise((resolve) => setTimeout(resolve, 500, 'slow'));


const promises = [promise1, promise2, promise3];


Promise.any(promises).then((value) => console.log(value));



2)AggregateError:

The AggregateError object represents an error when several errors need to be wrapped in a single error. 

It is thrown when multiple errors need to be reported by an operation,

for example by Promise.any(), when all promises passed to it reject.


Example:

Promise.any([

  Promise.reject(new Error("some error")),

]).catch(e => {

  console.log(e instanceof AggregateError); // true

  console.log(e.message); // "All Promises rejected"

  console.log(e.name);  // "AggregateError"

  console.log(e.errors); // [ Error: "some error" ]

});


Creating an AggregateError:


try {

  throw new AggregateError([

    new Error("some error"),

  ], 'Hello');

} catch (e) {

  console.log(e instanceof AggregateError); // true

  console.log(e.message);// "Hello"

  console.log(e.name); // "AggregateError"

  console.log(e.errors);// [ Error: "some error" ]

}


3)String.prototype.replaceAll():

The replaceAll() method returns a new string with all matches of a pattern replaced by a replacement. The pattern can be a string or a RegExp, and the replacement can be a string or a function to be called for each match.


The original string is left unchanged.


const p = 'The quick brown fox jumps over the lazy dog. If the dog reacted, was it really lazy?';


const regex = /dog/gi;


console.log(p.replaceAll(regex, 'ferret'));

// expected output: "The quick brown fox jumps over the lazy ferret. If the ferret reacted, was it really lazy?"


console.log(p.replaceAll('dog', 'monkey'));

// expected output: "The quick brown fox jumps over the lazy monkey. If the monkey reacted, was it really lazy?"



4)Logical assignment operators &&=, ||=, and ??= :

 

a)&&=

The logical AND assignment (x &&= y) operator only assigns if x is truthy.

Example:

let a = 1;

let b = 0;


a &&= 2;

console.log(a);

// expected output: 2


b &&= 2;

console.log(b);

// expected output: 0


b)||=

The logical OR assignment (x ||= y) operator only assigns if x is falsy.


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"



c)??=

The logical nullish assignment (x ??= y) operator only assigns if x is nullish (null or undefined).


const a = { duration: 50 };


a.duration ??= 10;

console.log(a.duration);

// expected output: 50


a.speed ??= 25;

console.log(a.speed);

// expected output: 25


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