Type Systems & Props Design - Exploring PropTypes, TypeScript, Flow & Reason

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Type Systems & Props Design   Exploring PropTypes, TypeScript, Flow & Reason

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Let’s start without types

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A or B or C

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easy to fix … is it though?

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Type systems to the rescue!

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PropTypes.string.isRequired;

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PropTypes.string.isRequired;

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PropTypes.oneOf(["down", "up"]).isRequired;

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export enum Direction { Up = "up", Down = "down" } interface Props { direction: Direction; } import { Direction } from "./Arrow";

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interface Props { direction: "up" | "down"; }

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interface Props { direction: "up" | "down"; }

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type direction = Down | Up;

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A{x} or B{x, y} or C

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Draft{content}  Post{content, publishedAt}

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interface DraftPost { status: "draft"; content: String; } interface PublishedPost { status: "published"; content: String; publishedAt: Date; } type Props = DraftPost | PublishedPost;

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export default function Post(props: Props) { switch (props.status) { case "draft": return

{props.content}

; case "published": return

{props.content}{props.publishedAt}

; } }

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Discriminated Unions

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Draft{status, content}  Post{status, content, publishedAt}

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interface DraftPost { status: "draft"; content: String; } interface PublishedPost { status: "published"; content: String; publishedAt: Date; } type Post = DraftPost | PublishedPost; interface Props { post: Post; }

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type DraftPost = { status: "draft", content: string }; type PublishedPost = { status: "published", content: string, publishedAt: Date }; type Props = DraftPost | PublishedPost;

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export default function Post(props: Props) { switch (props.status) { case "draft": return

{props.content}

; case "published": return

{props.content}{props.publishedAt}

; default: return null; } }

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type DraftPost = {| status: "draft", content: string |}; type PublishedPost = {| status: "published", content: string, publishedAt: Date |}; type Props = DraftPost | PublishedPost;

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Disjoint Unions

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Draft{status, content}  Post{status, content, publishedAt}

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type post = | Draft(string) | Published(string, int);

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let component = ReasonReact.statelessComponent("Arrow"); let make = (~post: post, _children) => { ...component, render: _self => switch (post) { | Draft(content) =>

content->s

| Published(content, timestamp) =>

content->s timestamp->string_of_int->s

}, };

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Variants

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Draft(content)  Post(content, publishedAt)

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Render Props

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query={getProfile}> {({ data, loading, error }) => { if (loading) return "Loading …"; if (error) return "Loading …"; if (!data) return null; return

{data.user.name}

; }} ;

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query={getProfile}> {({ result }) => { switch (result.type) { case "loading": return "Loading …"; case "error": return "Sorry, something went wrong"; case "data": return