Is basically telling what type something is.
For example let say we have a box,
and we want to tell people to only put eggs in the box.
let myBox; // 📦
In real life we would put a sticker in the box saying "only eggs
please 📄", in TypeScript we do the same, we add a "type" saying what something is and only accepts.
Variable Type value
┌────┴─────┐ ┌────┴─────┐ ┌───┴───┐
let myBox_📦 : onlyEggs_📄 = "🥚🥚🥚";
↑ ↑
Separator Assignment operator
There are 3 basic types in TypeScript
let isDone: boolean = false; // 😀 or 😟
let lines: number = 42; // 0️⃣1️⃣2️⃣3️⃣4️⃣5️⃣...
let name: string = "John"; // 📃
When it's impossible to know, there is the "Any" type
let notSure: any = 4; // 🤷♂️ Not sure
notSure = "I'm a string"; // I can change it later
notSure = false; // maybe a boolean
There are typed arrays
let list: number[] = [1, 2, 3];
// or with emojis:
Only chickens please!
┌─┴─┐
let chickens: 🐔[] = [🐣,🐤,🐥,🐓];
Alternatively you can use Array which It's same as Type[]
let list: Array<number> = [1, 2, 3];
// or with emojis
let listOfChickens: Array<🐔> = [🐣,🐤,🐥,🐓];
Enumerations also known as enums:
enum Square { Red, Green, Blue }; // 🟥, 🟩, 🟦
// This can be understood better by seeing what Enumerations
// are compiled to in JavaScript:
Square = {
0 : 'Red',
1 : 'Green',
2 : 'Blue',
Red : 0,
Green : 1,
Blue : 2,
};
// Now that you know is just an object,
// you can access it by name or number.
console.log( Square.Green ); // 🟩
console.log( Square[2] ); // 🟥
// or in a more complex way
let c: Square = Square.Blue;
console.log( Square[c] ); // 🟦
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