How to model your 🤪 data with
Michał Michalczuk
TypeScript
JavaScript that scales
TypeScript
ES6
ES5
- Superset of JS
- Compiles to JS
- JavaScript is a legal TypeScript
- Optionally statically typed
Type systems
| Lang | Types check | Run time safety |
|---|---|---|
|
|
Dynamic | Weak |
|
|
Static | Weak |
|
|
Static | Strong |
No extra memory footprint
TypeScript type system
Structural type system*
As strict as you want to
Structural
type Foo = {
foo: string;
handleStuff: () => void;
}
type Bar = {
foo: string;
}
let foo: Foo = {
foo: 'foo',
handleStuff: () => ({})
};
// works, struc. of `Bar` is subset
const bar: Bar = foo;
// won't compile.
// `handleStuff` is missing
foo = bar;
class Foo {
public string Foo { get; set; }
}
class Bar {
public string Foo { get; set; }
}
Foo foo = new Foo { Foo = "foo" };
// won't compile.
// Its different type
Bar bar = foo;
Nominal
#life
let foo = {
foo: 'foo',
handleStuff: () => ({})
};
const bar = 5;
bar = foo;
foo = bar;
Structural type system*
Michał Michalczuk
@michalczukm
Senior Software Engineer
Spartez / Atlassian
Jira Cloud
Modeling data
with
🤔
You
are responsible
for your models
No matter how 💩 is data
Let's take a look at some problems challenges with our data models
😈
Imagine this data
[
{
"id": 1,
"name": "Fancy product",
"type": "stock",
"price": 100,
"amountInStock": 101
},
{
"id": 2,
"name": "Ultimate product",
"type": "marketing",
"price": 200,
"marketingName": "GameChanger2000",
"description": "our new ultimate product!"
},
{
"id": 3,
"name": "Another product",
"type": "stock",
"price": 300,
"amountInStock": 301
}
]Only for "stock"
product
Only for "marketing"
product
Where is the 💩 ?
Write a model
// 😢
type Product = {
id: string,
type: 'stock' | 'marketing',
description?: string, // marketing only
marketingName?: string, // marketing only
price: number,
amountInStock?: number // stock only
};Problems:
- 😢 if-ing the optional fields
- 😢 don't know scenarios when fields are filled
⚡️Improve: Discriminated union type
⚡️Improve: Avoid fields duplication
Imagine - support multiple API versions
// 😢
type Client = {
id: string,
name: string,
version: number,
WasCreatedOnDate?: Date, // removed in v2
createdOnUTC?: string, // v2 only
refId?: string // v2 only
};Problems:
- 😢 if-ing the optional fields
- 😢 don't know when fields are filled
⚡️Quick improve: disc. union type again
⚡️Better way: Type helpers
Doctor, I have too many types 🥵
// this is just internal type, it should never be used outside `Phone`
type PhoneFeatures = {
isWaterproof: boolean,
ramAmount: number,
cpu: string
};
export type Phone = {
id: string,
features: PhoneFeatures,
promotedFeature: 'isWaterproof' | 'ramAmount' | 'cpu'
}Problems:
- 😢 types pollution
- 😢 types can be exposed without their "context"/"purpose"
⚡️ Inline + index type
type Phone = {
id: string,
features: {
isWaterproof: boolean,
ramAmount: number,
cpu: string
},
promotedFeature: 'isWaterproof' | 'ramAmount' | 'cpu'
}
function handle(features: Phone['features']) {
features.isWaterproof;
}(parameter) features: {
isWaterproof: boolean;
ramAmount: number;
cpu: string;
}💩
⚡️Index types: Avoid types pollution
⚡️More index types examples
About client... imagine this
[
// one client row
[
{
"id": 1
},
{
"clientId": "100",
"revenue": 12345
},
{
"country": "Poland",
"phoneNumber": "000-000-000"
}
],
...
]⚡️What about tuples
What if you..
don't want to add typings for some fields 😱
Why?
- I'm just passing them through my app/service
- I only want to show a shape, writing/maintaining those fields types not make sense
- ... any other GOOD reason 😊
any
- literally anything
- can access/call anything
- can assign anything
unknown
- literally unknown 😎
- cannot access/call at all
- can assign anything
- Mostly can be avoided
- Bad practice
- Your last hope
- Perfect for only "passing" stuff
- "Safe" - you won't do anything stupid
⚡️In `unknown` we trust
class
- compiles to JS class/proto
- don't use it for describing data
type
- compilation time only
- has to be unique in scope
- type/data modeling
interface
- compilation time only
- interfaces with same name merges
- use if you want to implement it
Something more?
How about this data
[
{
"id": 1,
"name": "Client 1",
"continent": "AF"
},
{
"id": 2,
"name": "Client 2",
"continent": "OC"
},
{
"id": 3,
"name": "Client 3",
"continent": "EU"
}
]Continent
acronym
We can describe it with type
// 😢
type Client = {
id: string,
name: string,
continent: 'AF' | 'AN' | 'AS' | 'EU' | 'NA' | 'OC' | 'SA';
}Problems:
- 😢 no value type, should be enumerated
- 😢 why not meaningfull names over API values
⚡️Improve: String-based enum
😇 Good enums
😈 Tricky enums
😱
Speaking of enums and types.
Where to put types? 🤔
*.d.ts
😰Living on the edge
😰Living on the edge
export enum Continent {
Africa = 'AF',
Antarctica = 'AN',
Asia = 'AS',
Europe = 'EU',
NorthAmerica = 'NA',
Oceania = 'OC',
SouthAmerica = 'SA'
}my-types.d.ts
export enum Continent {
Africa = 'AF',
Antarctica = 'AN',
Asia = 'AS',
Europe = 'EU',
NorthAmerica = 'NA',
Oceania = 'OC',
SouthAmerica = 'SA'
}my-model.ts
"use strict";
var Continent;
(function (Continent) {
Continent["Africa"] = "AF";
Continent["Antarctica"] = "AN";
Continent["Asia"] = "AS";
Continent["Europe"] = "EU";
Continent["NorthAmerica"] = "NA";
Continent["Oceania"] = "OC";
Continent["SouthAmerica"] = "SA";
})(Continent || (Continent = {})); compile
compile
😱
😰Living on the edge
declare const PolandISOCode = 'PL';my-types.d.ts
declare const PolandISOCode = 'PL';my-model.ts
"use strict"; compile
compile
😱
😱
Hey! what about
Algebraic Data Types
Algebraic Data Types
Product
Sum
C(A | B) = C(A) + C(B)C([A, B]) = C(A) x C(B)- tuples
- records (index)
- union type
Summary time!
- use TS rich types toolset
- type, type and type
- remember which TS elements have JS dist.
- avoid types pollution
- be rational
- don't make your code look like git conflict
Feedback?
Yes please
