Sean Groff

ES2020: The Good Parts

May 11, 2020

Introduction

I avoid a majority of JavaScripts pitfalls by following established best practices. Some parts of JavaScript I have no use for personally or professionally. This leaves my toolbelt with only “The Good Parts” of JavaScript. This is mostly subjective but I follow the basic rules of functional programming, well known established best patters, and most importantly code readability. With all of this in mind, I don’t throw all the shiny brand new toys in my toolbelt. This post is going to go over the new features from the latest version of JavaScript I’ll be using immediately.

Optional Chaining

The optional chaining syntax ?. allows you to safely access deeply nested object properties whether the property exists or not. If the object property does not exist, undefined will be returned.

Problem

let mammals = {
  cat: { legs: 4, tail: true, carnivore: true },
  dog: { legs: 4, tail: true, carnivore: true, petFriendly: true },
}

function getGoatLegsCount() {
  let count = mammals.goat.legs
  return count || 'Unknown'
}

let goatLegsCount = getGoatLegsCount() // Uncaught TypeError: Cannot read property 'legs' of undefined

Solution before Optional Chaining

let mammals = {
  cat: { legs: 4, tail: true, carnivore: true },
  dog: { legs: 4, tail: true, carnivore: true, petFriendly: true },
}

function getGoatLegsCount() {
  let count = mammals && mammals.goat && mammals.goat.legs // 😰
  return count || 'Unknown'
}

let goatLegsCount = getGoatLegsCount() // 'Unknown'

Solution with Optional Chaining

let mammals = {
  cat: { legs: 4, tail: true, carnivore: true },
  dog: { legs: 4, tail: true, carnivore: true, petFriendly: true },
}

function getGoatLegsCount() {
  let count = mammals.goat?.legs // 🔥
  return count || 'Unknown'
}

let goatLegsCount = getGoatLegsCount() // 'Unknown'

Notes

Optional chaining also works on function calls and arrays but I don’t prefer optional chaining for these currently. Here’s an example of optional chaining on a function call directly from MDN.

// Written as of ES2019
function doSomething(onContent, onError) {
  try {
    // ... do something with the data
  } catch (err) {
    if (onError) {
      // Testing if onError really exists
      onError(err.message)
    }
  }
}
// Using optional chaining with function calls
function doSomething(onContent, onError) {
  try {
    // ... do something with the data
  } catch (err) {
    onError?.(err.message) // no exception if onError is undefined
  }
}

In this scenario, I prefer the if statement but as Optional Chaining becomes more widely used that may change.

Nullish Coalescing Operator

The nullish coalescing operator ?? provides a short syntax that returns the left-hand side operand if the operand is defined (NOT null or undefined), otherwise, the right-hand side operand is returned. If you’re familiar with the logical or || operator you’re probably asking yourself what the point of this new silly named operator is? Notice I used the word defined? This is different than a falsy value.

Problem

A common bug I’m certainly guilty of writing is using the || operator to account for falsy values but forgetting to handle the number 0 which is a falsy value.

Solution before Nullish Coalescing

let nothing = null
let zero = 0
let five = 5

function getSuperSaiyanPowerLevel(number) {
  return number || 9000
}

getSuperSaiyanPowerLevel(nothing) // 9000 ✅
getSuperSaiyanPowerLevel(zero) // 9000 🐛
getSuperSaiyanPowerLevel(five) // 5 ✅

Solution with Nullish Coalescing

let nothing = null
let zero = 0
let five = 5

function getSuperSaiyanPowerLevel(number) {
  return number ?? 9000
}

getSuperSaiyanPowerLevel(nothing) // 9000 ✅
getSuperSaiyanPowerLevel(zero) // 0 ✅
getSuperSaiyanPowerLevel(five) // 5 ✅

Notes

The precedence of the ?? operator is pretty low so I add parenthesis whenever I’m writing a complex expression. As a safety feature JavaScript prevents you from using ?? together with && and || operators.

let foo = 1 && 2 ?? 3; // Syntax error⛔️

To get around this you can add parenthesis to the expressions

let foo = (1 && 2) ?? 3 // 2 ✅

I think mixing ??, &&, || is a code smell but I’m not your boss!

Can I use these?

Conclusion

As a mostly frontend engineer, I don’t plan on using the remainder of the new ES2020 features very often. Except for Promise.allSettled() which I may be able to utilize in React to hide loading spinners that should disappear when a series of promises resolves 🤔.

Thanks for reading!

I am Sean, a Software Engineer in Kansas City passionate about React and JavaScript.

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