robertcoopercode

enum Sizes {
    Small = 1,
    Medium,
    Large,
}

Sizes.Small; // => 1
Sizes.Medium; // => 2
Sizes.Large; // => 3

robertcoopercode

let whoKnows: any = 4; // assigned a number

whoKnows = 'a beautiful string'; // can be reassigned to a string
whoKnows = false; // can be reassigned to a boolean

robertcoopercode

const darkestPlaceOnEarth = (): void => {
    console.log('Marianas Trench');
};

robertcoopercode

let anUndefinedVariable: undefined = undefined;
let aNullVariable: null = null; 

robertcoopercode

// Variable initialization
let x = 10; // x is given the number type

robertcoopercode

// Default function parameters
const tweetLength = (message = 'A default tweet') => {
    return message.length;
}

robertcoopercode

function add(a: number, b: number) {
    return a + b;
}

const result = add(2, 4);

result.toFixed(2); // ✅
result.length; // ❌ - length is not a property of number types

robertcoopercode

let list = [10, 22, 4, null, 5];

list.push(6); // ✅
list.push(null); // ✅
list.push('nope'); // ❌ - type 'string' is neither of type 'number' or 'null'

robertcoopercode

let aBoolean: boolean = true;
let aNumber: number = 10;
let aString: string = 'woohoo';

robertcoopercode

// First method is using the square bracket notation
let messageArray: string[] = ['hello', 'my name is fred', 'bye'];

// Second method uses the Array keyword notation
let messageArray: Array<string> = ['hello', 'my name is fred', 'bye'];