In 2020 JavaScript gained a new feature – optional chaining. It solves a problem we've had ... forever. With many workarounds and standard solutions over the years.
TIL you can use optional chaining on function calls 🤯 pic.twitter.com/rfjw5A5atn
— Swizec Teller (@Swizec) June 23, 2021
The problem optional chaining solves
You get an object like this:
const object = {
greet: "hai",
deepProp: {
greet: "hello",
deeperProp: {
greet: "ohai",
},
},
}
JSON response from an API or reading from a database. Perhaps a blob you've built up on the frontend.
How do you access the 3rd level greet, if object, deepProp, and deeperProp might be undefined?
You could rely on JavaScript's evaluation semantics. Last value from expression is returned.
const greeting =
object &&
object.deepProp &&
object.deepProp.deeperProp &&
object.deepProp.deeperProp.greet
Confusing for newbies, annoying to write, easy to get wrong. Exploding complexity to boot.
A clearer way to write that are conditionals:
let greeting = undefined
if (object) {
if (object.deepProp) {
if (object.deepProp.deeperProp) {
greeting = object.deepProp.deeperProp
}
}
}
Clearer, more verbose, nobody writes this in production code. Feels weird to use conditionals for assignment. 🤷
Another common approach is to use a library like Lodash:
const greeting = _.get(object, "deepProp.deeperProp.greet")
Personally not a fan. Feels unnecessary.
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Use optional chaining
With optional chaining you can do this natively:
const greeting = object?.deepProp?.deeperProp?.greet
😍
You've probably seen that before. Everyone's been very excited after wishing this existed for 10+ years.
But you might've missed that the operator is ?., not ?. This is important because you can optionally chain anything 🤯
Function calls:
object?.deepProp?.function?.(args)
Array access:
object?.deepProp?.deepArray?.[5]
And even expressions:
object?.deepProp?.[console.log("runs if deepProp defined")]
Please don't use that last one 😅
Cheers,
~Swizec
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Want to become a JavaScript expert?
Learning from tutorials is great! You follow some steps, learn a smol lesson, and feel like you got this. Then you go into an interview, get a question from the boss, or encounter a new situation and o-oh.
Shit, how does this work again? 😅
That's the problem with tutorials. They're not how the world works. Real software is a mess. A best-effort pile of duct tape and chewing gum. You need deep understanding, not recipes.
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