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    Quick tip about JavaScript's optional chaining operator

    People on twitter loved this trick I learned from a coworker's pull request the other day. You might like it too.

    Swizec Teller writing a Manning book avatarSwizec Teller writing a Manning book@Swizec
    TIL this works #javascript
    Tweet media

    You can use ?.() to call a potentially undefined function 🤯 Works for array access too. ?.[]

    The common use case for optional chaining is object access. If you're like me, that gave you the wrong mental model of the operator.

    const bird = {
    name: "Kiwi",
    species: ["Parrot"],
    }
    // prints undefined
    console.log(user.address?.street)

    If . is chaining, then ? is the optional part. Obvious.

    And wrong. ?. is the optional chaining operator for JavaScript.

    That gives you the flexibility to use it anywhere. Function calls, array access, ... I can't think of others.

    Optional chaining doesn't guarantee that what you're using supports the way you're holding it. Optional chaining is not a type check, it's an ergonomic way to hold null and undefined values.

    Best used in combination with TypeScript, which guarantees (ish) the correct type of underlying value. Like this:

    type Bird = {
    name: string
    species?: string[]
    address?: {
    continent: string
    environment: string
    }
    }
    const BirdButton = (props: { bird: Bird; onClick?: Function }) => {
    const { bird, onClick } = props
    return (
    <button onClick={() => onClick?.()}>
    {bird.name} is a {bird.species?.[0]} from the {bird.address?.environment}{" "}
    of {bird.address?.continent}
    </button>
    )
    }

    The ? in TypeScript types means "possibly undefined". The ?. in JavaScript lets you use that ergonomically. No more onClick && onClick() 😍

    You can use <BirdButton> all these ways:

    <BirdButton bird={{ name: "Kiwi" }} />
    <BirdButton bird={{ name: "Kiwi" }} onClick={() => alert("hai")} />
    <BirdButton bird={{ name: "Kiwi", species: ["Parrot", "Conure"] }} />
    <BirdButton
    bird={{
    name: "Kiwi",
    species: ["Parrot", "Conure"],
    address: { continent: "Brazil", environment: "Jungle" },
    }}
    />

    Browser and server environment support is good except you need the latest Safari and recent NodeJS.

    Optional chaining browser support
    Optional chaining browser support

    Not a concern, if you're using a build step in your code like Babel or TSC. Make sure you regularly update your browserlist because I hear Babel turns ?. into lots of code.

    Cheers,
    ~Swizec

    PS: yes my example doesn't do well with partial bird info. It prints Kiwi is a from the of. But that's not the point of this email 😅

    Did you enjoy this article?

    Published on April 22nd, 2022 in JavaScript, Quicktip,

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