Future JavaScript: what is still missing?
In recent years, JavaScript has grown considerably in size. This blog post explores what’s still missing. Notes: I’m only listing the missing features that I find most important. Many others are useful, but there is also a risk of adding too much. My choices are subjective. Almost everything mentioned in this blog post is on TC39’s radar. That is, it also serves as a preview of a possible future J
JavaScript vs. TypeScript vs. ReasonML
In this blog post, I describe the pros and cons of three programming languages/dialects: JavaScript, TypeScript and ReasonML. My descriptions are based on recent experiences with TypeScript and ReasonML on a few smaller real-world projects and on years of experience with JavaScript. Before we take a look at the languages, let’s first consider the pros and cons of static typing, given that TypeScri
Pattern matching in ReasonML: destructuring, `switch`, `if` expressions
There are many more ways of creating patterns # ReasonML supports more complex data types than just tuples. For example: lists and records. Many of those data types are also supported via pattern matching. More on that in upcoming blog posts. Pattern matching via let (destructuring) # You can do pattern matching via let. As an example, let’s start by creating a tuple: # let tuple = (7, 4); let t
Currying is not idiomatic in JavaScript
Update 2017-11-18a: I worded a few things more carefully, to make it clear that I don’t hate functional programming (I’m a fan). Update 2017-11-18b: I added subsections to Sect. “Currying is in conflict with some of JavaScript’s foundations”. In this blog post I explain why, in my opinion, currying is in conflict with some of JavaScript’s foundations. Recommended reading if you are not sure what c
Using ES modules natively in Node.js
Update 2018-12-20: Warning: This blog post is outdated! Consult “ECMAScript modules in Node.js: the new plan” for the latest information. Update 2017-09-14: Major rewrite of Sect. “Checklist: things to watch out for”. New FAQ entries. Starting with version 8.5.0, Node.js supports ES modules natively, behind a command line option. Most of the credit for this new functionality goes to Bradley Farias
Passing data between Promise callbacks
In Promise-based code, there are usually many callbacks, each one having a separate scope for variables. What if you want to share data between those callbacks? This blog post describes techniques for doing so. The problem # The following code illustrates a common problem with Promise callbacks: The variable connection (line A) exists in one scope, but needs to be accessed in other scopes (line B
ES2019: optional catch binding
The proposal “Optional catch binding” by Michael Ficarra is at stage 4 and therefore part of ECMAScript 2019. This blog post explains how it works. Overview # The proposal allows you to do the following: try { ··· } catch { ··· } That is useful whenever you don’t need the binding (“parameter”) of the catch clause: try { ··· } catch (error) { ··· } If you never use the variable error, you may as w
Module specifiers: what’s new with ES modules?
Update 2018-12-20: Warning: This blog post is outdated! Consult “ECMAScript modules in Node.js: the new plan” for the latest information. Update 2017-05-11: Complete rewrite of Sect. “Why a new filename extension for ES modules?”. This blog post describes how module specifiers (the path-like IDs of modules) change with ECMAScript modules (ESM). There are a few subtle differences, compared to the f
ES2019: Functional pattern – flatMap
Update 2019-01-29: The following new Array methods were just added to ECMAScript 2019 (based on a proposal by Michael Ficarra, Brian Terlson, Mathias Bynens): The new Array method .flatMap() is equivalent to the function flatMap() described in this blog post. The new Array method .flat() is equivalent to the function flatten() described in this blog post. In this blog post, we look at the operatio
Feature watch: ECMAScript 2018
Check out my book (free online): “Exploring ES2018 and ES2019”. Buy it now and get all future updates. The feature set of ECMAScript 2018 was finalized during the latest TC39 meeting (23-25 January 2018). This blog post describes it. A word on ECMAScript versions # Note that since the TC39 process was instituted, the importance of ECMAScript versions has much decreased. What really matters now is
ECMAScript 2017 (ES8): the final feature set
Check out my book (free online): “Exploring ES2016 and ES2017”. Update 2017-01-29: At the TC39 meeting in January 2017, the last feature of ECMAScript 2017, “Shared memory and atomics” advanced to stage 4. That means that its feature set is now complete, as listed below. The features of ECMAScript 2017 # Major new features: Async Functions (Brian Terlson) Shared memory and atomics (Lars T. Hansen
ES proposal: Shared memory and atomics
The ECMAScript proposal “Shared memory and atomics” by Lars T. Hansen has reached stage 4 this week and will be part of ECMAScript 2017. It introduces a new constructor SharedArrayBuffer and a namespace object Atomics with helper functions. This blog post explains the details. Update 2017-02-24: Complete rewrite of Sect. 4, “Atomics: safely accessing shared data”. Parallelism vs. concurrency # Be
Making transpiled ES modules more spec-compliant
A proposed “spec mode” for Babel makes transpiled ES modules more spec-compliant. That’s a crucial step in preparing for native ES modules. You’ll also learn how ES modules and CommonJS modules will interoperate on Node.js and how far along ES module support is on browsers and Node.js. Update 2017-05-08: follow-up blog post: Module specifiers: differences between CJS and ESM Transpiling ES modules
ES2020: `import()` – dynamically importing ES modules
Warning: This blog post is outdated. Instead, read section “Loading modules dynamically via import()” in “JavaScript for impatient programmers”. The ECMAScript proposal “import()” by Domenic Denicola is at stage 4 and part of ECMAScript 2020. It enables dynamic loading of ECMAScript modules and is explained in this blog post. ECMAScript modules are static # ECMAScript modules are completely stati
Tree-shaking with webpack 2 and Babel 6
Rich Harris’ module bundler Rollup popularized an important feature in the JavaScript world: tree-shaking, excluding unused exports from bundles. Rollup depends on the static structure of ES6 modules (imports and exports can’t be changed at runtime) to detect which exports are unused. Tree-shaking for webpack is currently in beta. This blog post explains how it works. The project we are going to e
Tips for using async functions (ES2017)
This blog post gives tips for using async functions. If you are unfamiliar with them, you can read chapter “Async functions” in “Exploring ES2016 and ES2017”. Know your Promises # The foundation of async functions is Promises. That’s why understanding the latter is crucial for understanding the former. Especially when connecting old code that isn’t based on Promises with async functions, you ofte
Tips for using async functions (ES2017)
This blog post gives tips for using async functions. If you are unfamiliar with them, you can read chapter “Async functions” in “Exploring ES2016 and ES2017”. Know your Promises # The foundation of async functions is Promises. That’s why understanding the latter is crucial for understanding the former. Especially when connecting old code that isn’t based on Promises with async functions, you ofte
ES2018: asynchronous iteration
Warning: This blog post is outdated. Instead, read chapter “Asynchronous iteration” in “JavaScript for impatient programmers”. This blog post explains the ECMAScript proposal “Asynchronous Iteration” by Domenic Denicola and Kevin Smith. It has reached stage 4 on 2018-01-25 and is part of ECMAScript 2018. Asynchronous iteration # With ECMAScript 6, JavaScript got built-in support for synchronously
ES proposal: `global`
Warning: This blog post is outdated. Instead, read section “globalThis” in “JavaScript for impatient programmers”. The ECMAScript proposal “global” by Jordan Harband is currently at stage 3. It provides a new standard way of accessing the global object. Referring to the global object # The following are a few popular ways of referring to the global object: Global variables: Global variable window
Six nifty ES6 tricks
In this blog post, I show six tricks enabled by new ES6 features. At the end of each section, I point to related material in my book “Exploring ES6” (which is free to read online). Enforcing mandatory parameters via parameter default values # ES6 parameter default values are only evaluated when they are actually used. That lets you enforce that a given parameter be provided: /** * Called if a par
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