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

Badly designed props can lead to components that are frustrating to use. While there are a couple patterns to make components more pleasant to use, ultimately it needs a type system in combination with a good editor integration for an even better developer experience. Yet not all type systems are the same. They offer different features and therefore lead to different experiences.

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1. Type Systems &
   Props Design
   

   Exploring PropTypes, TypeScript, Flow & Reason
   

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2. Let’s start without types
   

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3. 
   

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4. 
   

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5. 
   

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6. 
   

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7. 
   

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8. 
   

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9. 
   

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10. 
    

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11. 
    

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12. 
    

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13. 
    

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15. A or B or C
    

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16. easy to fix … is it though?
    

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17. Type systems to the rescue!
    

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18. 
    PropTypes.string.isRequired;
    

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19. PropTypes.string.isRequired;
    
    

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

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

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

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

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31. 
    type direction = Down | Up;
    

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

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34. Draft{content}

    Post{content, publishedAt}
    

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

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37. 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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39. Discriminated Unions
    

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40. Draft{status, content}

    Post{status, content, publishedAt}
    

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41. 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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42. post={{
    status: "published",
    content: "Unicorns & Cats",
    publishedAt: new Date()
    }}
    />
    

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

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

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49. Disjoint Unions
    

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50. Draft{status, content}

    Post{status, content, publishedAt}
    

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51. post={{
    status: "published",
    content: "Unicorns & Cats",
    publishedAt: new Date()
    }}
    />
    

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

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54. 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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56. Variants
    

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57. Draft(content)

    Post(content, publishedAt)
    

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58. Render Props
    

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

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62. 
    ...{
    ({result}) =>
    switch (result) {
    | Loading => "Loading"->s
    | Error(error) => error##message->s
    | Data(response) => response##user##name->s
    }
    }
    ;
    

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64. notifyOnNetworkStatusChange
    

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65. Usage & Complexity
    Type your Code
    

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66. The End
    @nikgraf
    

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