Sådan tilføjes trinvist Flow til en eksisterende React-app

Flow er en statisk checker til Javascript. Dette indlæg er beregnet til dem, der har hørt om Flow, men endnu ikke har forsøgt at bruge det i en React-app. Hvis dette er første gang, du har hørt om Flow, kan jeg anbefale disse fire indlæg af Preethi Kasireddy som en god introduktion.

En god ting ved Flow er, at det er muligt at bruge det trinvist. Du behøver ikke at omlægge et eksisterende projekt helt for at begynde at bruge det. Det kan kun føjes til nye filer eller langsomt forsøges i eksisterende filer for at se, om det giver fordele for dit specifikke projekt, inden du forpligter dig fuldt ud.

Da opsætningen af ​​et nyt værktøj ofte kan være den mest udfordrende, vil vi i dette indlæg tage et eksisterende projekt og gå gennem opsætningen af ​​tilføjelse af Flow. En generel introduktion til syntaks er dækket af det andet af Preethis indlæg, og Flow-dokumenterne er også meget læselige.

Vi bruger dette eksemplar repo med to mapper til før og efter flow. Det bruger Skyscanners tilpassede Create React App-script backpack-react-scriptsparret med deres brugerdefinerede rygsækkomponenter. Dette har til formål at skabe eksempler, der er mere komplekse end enkeltuddrag, men alligevel læsbare, selvom du ikke er bekendt med dem.

Den nøjagtige karakter af appen er uvigtig i forhold til at se forskellen mellem dens implementering uden og med Flow. Meget få filer ændres her, men de er ofte de mest frustrerende at få ret!

Lad os gå igennem hvert trin og derefter se på konvertering af eksemplets komponenter.

Installer de vigtigste afhængigheder

Ved siden af ​​Flow selv skal du installere babel-cli og babel-preset-flow, så babel kan fjerne typebemærkningerne ved kompilering.

npm install flow-bin babel-cli babel-preset-flow --save-dev

Opsæt Babel

For at disse skal træde i kraft, skal du oprette en .babelrcfil eller føje til din eksisterende .babelrcfølgende konfiguration:

{ "presets": ["flow"] }

Opsæt scripts

Hvis du bruger kroge, f.eks. Et fortest-script, kan du opdatere disse samt tilføje det grundlæggende Flow-script til dit package.json:

"scripts": { "flow": "flow", "pretest": "npm run flow && npm run lint" }

Generer en flowconfig

Hvis du kører flow for første gang, kan du generere en skabelon .flowconfigved at køre npm run flow init. I vores eksempel kan vi se, at vi udvider det til at tilføje følgende:

Ignorer mønstre

For at undgå Flow-parsering af dine node-moduler og build-output kan disse let ignoreres.

[ignore].*/node_modules/*.*/build/*

Tilføj understøttelse af CSS-moduler

Hvis du bruger CSS-moduler, skal deres type specificeres, for at Flow kan forstå dem, ellers får du denne fejl:

Dette gøres i to trin. Først føjes nedenstående til din .flowconfig:

[libs] ./src/types/global.js // this can be any path and filename you wish [options] module.name_mapper='^\(.*\)\.scss$' -> 'CSSModule' module.system=haste

Og for det andet oprettes en CSS-modultype i den fil, der henvises til [libs].

// @flow declare module CSSModule { declare var exports: { [key: string]: string }; declare export default typeof exports; }

Synkroniser med andre liners, der bruges

I eksempelprojektet bruges ESLint allerede til at levere standardfodring. Der er nogle indledende konfigurationstrin nødvendige for at få ESLint til at spille pænt med Flow, og nogle senere på grund af de specifikke typer, der bruges i dette projekt.

For generel opsætning tilføjes følgende til vores .eslintrc:

"extends": [ "plugin:flowtype/recommended" ], "plugins": [ "flowtype" ]

Udvidelser, der er specifikke for dette eksempel, og de fejl, de undgår, vil blive dækket mod slutningen af ​​dette indlæg.

Flow-typede libdefs

Det sidste stykke opsætning er at gøre sig klar til brug libdefsoprettet ved hjælp af flow-typedNPM-pakken. Dette bruges til at oprette definitioner for installerede nodemoduler og opretter som standard disse filer i et flow-typed/bibliotek.

Vi gør ønsker at begå denne fil, men ønsker ikke ESLint at fnug det. Dette skaber et problem, som tidligere vores linting script i vores package.jsoner indstillet til at bruge vores .gitignoretil at vide, mens filer ESLint også bør ignorere:

"lint:js": "eslint . --ignore-path .gitignore --ext .js,.jsx",

Vi vil nu ændre dette, da vi ønsker, at ESLint også ignorerer den flow-typed/katalog, der skal oprettes . Vi kan ændre vores script til:

"lint:js": "eslint . --ext .js,.jsx",

Dette betyder, at det nu vil falde tilbage til at bruge en .eslintignorefil, så vi er nødt til at oprette denne, duplikere, hvad der er i vores .gitignore, og tilføje den ekstra mappe, der skal ignoreres til den.

Endelig skal vi installere flow-types. Vi gør dette globalt.

npm install flow-typed -g

libdefskan enten være fulde definitioner eller stubs, der accepterer alle typer. En liste med fulde definitioner opretholdes. For at se om der er en tilgængelig til en pakke, du bruger

flow-typed install [email protected]

og dette vil enten føje det til din flow-typedmappe eller bede dig om at oprette en stub ved hjælp af

flow-typed create-stub [email protected]

Hvis du vil oprette en fuld definition, kan du gøre det og også bidrage med det tilbage til lageret, så det er tilgængeligt for andre udviklere.

En enkel proces at følge er kun at oprette, libdefssom de specifikt kræves. For hver komponent, du konverterer til at bruge Flow, tilføj dens import ved hjælp af flow-typedpå det tidspunkt, er det ikke nødvendigt at tilføje typer til alle afhængigheder, hvis de ikke bruges i filer, hvor Flow også bruges.

Konvertering af eksisterende komponenter

Det er alt det generelle setup, nu kan vi se på at konvertere vores eksempler på komponenter!

Vi har to, en stateful komponent og en funktionskomponent. Samlet set skaber disse et banner, end der har noget tekst og en knap. Teksten på banneret kan klikkes for at åbne en popover, der indeholder en punkttegnet liste.

Tilføj flow-typede definitioner

For enhver komponent er det første trin at oprette flow-typeddefinitioner for enhver import af den komponent, vi arbejder i.

For eksempel, hvis vi kun havde import af

import React from 'react'; import BpkButton from 'bpk-component-button';

så ville vi prøve:

flow-typed install [email protected] on>

if it was not available, and it currently is not, then we would stub its definition:

flow-typed create-stub [email protected]

In the example repo we can see the list of all created definitions for the components we moved to using Flow. These were added one at a time as each component had Flow integrated with them.

Function Components

In our example without Flow we use PropTypes for some limited type checking and their ability to define defaultProps for use in development.

It may look a little complex on first glance, but there is relatively little that we need to change in order to add Flow.

To transform this to use Flow we can first remove the PropTypes import and definitions. The // @flow annotation can then be added to line one.

For this component we are only going to type check the props passed in. To do so we will first create a Props type, much cleaner than defining each prop individually inline.

type Props = { strings: { [string_key: string]: string }, onClose: Function, isOpen: boolean, target: Function, };

Here the latter three types are self-explanatory. As strings is an object of strings an object as a map has been used, checking each key and value in the object received to check that their types match, without having to specify their exact string keys.

The prop-types definitions can then be removed along with its import. As defaultProps are not tied to this import they can, and should, remain. *See the closing ESLint comments for any errors reported at this point.

The component should now look like this:

Stateful Components

Stateful components follow some slightly different declarations. As this component is more complex we will also look at declaring types for some additional aspects.

As before, first take a look at the component before adding Flow.

Props and State

As in the function component we first remove the propTypes definition and import, and add the // @flow annotation.

First we will take a look at adding types for Props and State. Again we will create types for these:

type Props = { strings: { [string_key: string]: string }, hideBannerClick: Function, }; type State = { popoverIsOpen: boolean, };

and specify that the component will use them:

class Banner extends Component { constructor(props: Props) { super(props); this.state = { popoverIsOpen: false, }; ... }; ... };

Next we hit our first difference between Function and Stateful components, defaultProps. In a Function component these were declared as we are used to, in Stateful components the external Banner.defaultProps syntax is removed, and instead the defaults are declared within the class:

class Banner extends Component { static defaultProps = { strings: defaultStrings, }; constructor(props: Props) { ... // the below is removed // Banner.defaultProps = { // strings: defaultStrings, // };

Constructor declarations

stringWithPlaceholder is declared within the constructor. Here we are not looking at why it is declared there (we will assume there is good reason), but rather to see whether flow can be added without any changes to the existing code.

If run in its existing state we would encounter the error Cannot get this.stringWithPlaceholder because property stringWithPlaceholder is missing in Banner [1].

To fix this we must add a single line inside the Banner class block, just beneath and outside of the constructor:

class Banner extends Component { constructor(props: Props) { super(props); this.state = { popoverIsOpen: false, }; this.stringWithPlaceholder = ... }; stringWithPlaceholder: string; ... };

This variable is created in the constructor but not passed in as props. As we are using Flow for type checking the props passed into the constructor, it requires everything within the constructor be type checked. It is known that Flow requires this, and this can be done by specifying their type in the class block.

At this point Props and State are complete. Let’s look at some quick additional examples of type checking within this component. *See the closing ESLint comments for any errors reported at this point.

Return, Event, and Node types

togglePopover takes no arguments, so a simple example of specifying no return value can be seen:

togglePopover = (): void => { ... };

keyboardOnlyTogglePopover returns nothing, but has a single parameter. This is an event, specifically a keypress event. SyntheticKeyboardEvent is used as

React uses its own event system so it is important to use the SyntheticEvent types instead of the DOM types such as Event, KeyboardEvent, and MouseEvent.
keyboardOnlyTogglePopover = (e: SyntheticKeyboardEvent): void => { ... };

Popover is defined in render() and returns an instance of the ListPopover Function component we looked a previously. We can specify its return type as a React Node. However, to be able to do so, we must first import it, as it is not accessible by default. There is more than one way to import it, one of which shown below:

import React, { Component } from 'react'; import type { Node } from 'react'; ... const Popover: Node = (  document.getElementById('ListPopoverLink')} /> );

Type checking imported React components

When Prop types have been declared in a component, they can be used when using that component within another. However, if you are using an index.js to export the first component then the flow, // @flow will need to be added to the index.

For example:

// @flow import ListPopover from './ListPopover'; export default ListPopover;

Marking props as optional

A prop can be marked as optional using the prop?: type syntax, for example:

type Props = { strings: { [string_key: string]: string }, hideBannerClick?: Function, };

This is supported, but no longer recommended by Flow. Instead all props should be left as required, with no ? , even if optional, as Flow automatically detects defaultProps and marks props with a default as optional internally.

In the section below we can see how manually marking props as optional can cause conflicts with other tools in some cases.

ESLint extensions, default props, and props validation error solutions

Two additions are made to our .eslintrc. For this project specifically you can simply accept their use, or read the detail below if you see any of the three errors:

  • x missing in props validation
  • error defaultProp "x" defined for isRequired propType
  • Cannot get strings.xxx because property xxx is missing in undefined

The rules added, with reasoning, are:

"react/default-props-match-prop-types": [ "error", { "allowRequiredDefaults": true } ]

When using objects as maps (in this case for the 'strings' prop) a missing in props validation error occurs. This is a bug and so is explicitly ignored here.

"react/default-props-match-prop-types": [ "error", { "allowRequiredDefaults": true }]

When using objects as maps complexities between ESLint, flow, and prop-types come into play.

strings is a required prop, passed as an object of strings. The flow type checks that for each entry in the object the string key is a string, and the value is a string. This is far more maintainable than having to list out the prop type of each specific key.

If the prop is marked as required in Flow then ESLint would error stating: error defaultProp "strings" defined for isRequired propType.

If the prop is manually marked as optional then Flow will error with Cannot get strings.xxx because property xxx is missing in undefined [1].

This is known and is due to refinement invalidation as JSX can transform method calls so Flow cannot be sure that xxx has not been redefined.

This leaves us with fixing the ESLint error. The rules above allows defaultProps to be defined while the Flow type is not marked as optional. Flow will understand this and convert it to optional. ESLint is marked to "allowRequiredDefaults": true, meaning that although ESLint sees the prop as required it will not error.

Final thoughts

Once over the initial hurdle of installation, Flow is fairly straightforward to use. The ability to add it incrementally definitely helps, rather than having to refactor an entire project in one go.

Hopefully the setup instructions and examples here prove useful if you are looking to try Flow out yourself.

Thanks for reading ?

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