13 posts tagged with "io19"

Several proposals expand the existing JavaScript class syntax with new functionality. This article explains the new public class fields syntax in V8 v7.2 and Chrome 72, as well as the upcoming private class fields syntax.

Here’s a code example that creates an instance of a class named IncreasingCounter:

const counter = new IncreasingCounter();
counter.value;
// logs 'Getting the current value!'
// → 0
counter.increment();
counter.value;
// logs 'Getting the current value!'
// → 1

Note that accessing the value executes some code (i.e., it logs a message) before returning the result. Now ask yourself, how would you implement this class in JavaScript? 🤔

ES2015 class syntax​

Here’s how IncreasingCounter could be implemented using ES2015 class syntax:

class IncreasingCounter {
  constructor() {
    this._count = 0;
  }
  get value() {
    console.log('Getting the current value!');
    return this._count;
  }
  increment() {
    this._count++;
  }
}

The class installs the value getter and an increment method on the prototype. More interestingly, the class has a constructor that creates an instance property _count and sets its default value to 0. We currently tend to use the underscore prefix to denote that _count should not be used directly by consumers of the class, but that’s just a convention; it’s not really a “private” property with special semantics enforced by the language.

Modern web applications often use phrases like “yesterday”, “42 seconds ago”, or “in 3 months” instead of full dates and timestamps. Such relative time-formatted values have become so common that several popular libraries implement utility functions that format them in a localized manner. (Examples include Moment.js, Globalize, and date-fns.)

BigInts are a new numeric primitive in JavaScript that can represent integers with arbitrary precision. With BigInts, you can safely store and operate on large integers even beyond the safe integer limit for Numbers. This article walks through some use cases and explains the new functionality in Chrome 67 by comparing BigInts to Numbers in JavaScript.