TS_BasicTypes

BasicTypes.ts

// Basic Types


// Boolean
let isDone: boolean = false


// Number
let decimal: number = 6
let hex: number = 0xf00d
let binary: number = 0b1010
let octal: number = 0o744


// String
let color: string = "blue"
color = 'red'
let fullName: string = `Bob Bobbington`
let age: number = 37
var sentence: string = `Hello, my name is ${fullName}.
I'll be ${ age + 1} years old next month.`
var sentence: string = "Hello, my name is " + fullName + ".\n\n" +
    "I'll be " + (age + 1) + " years old next month."


// Array
var list: number[] = [1, 2, 3]
var list: Array<number> = [1, 2, 3]
// var list: Array<string> = ["1", "2", "3"] // Variable 'list' must be of type 'number[]', but here has type 'string[]'.
console.log(list)


// Tuple
// Declare a tuple type
let x: [string, number]
// Initialize it
x = ["hello", 10] // OK
// Initialize it incorrectly
// x = [10, "hello"] // Error
console.log(x[0].substr(1)) // OK
// console.log(x[1].substr(1)) // Error, 'number' does not have 'substr'
x[3] = "world" // OK, 'string' can be assigned to 'string | number'
console.log(x[1].toString()) // OK, 'string' and 'number' both have 'toString'
// x[1] = true // Error, 'boolean' isn't 'string | number'


// Enum
enum Color1 { Red = 10, Green, Blue }
var c: Color1 = Color1.Green
console.log(c) // 11

enum Color2 { Red = 1, Green = 5, Blue = 4 }
var cc: Color2 = Color2.Green
console.log(cc) // 5

enum Color3 { Red = 1, Green, Blue }
let colorName: string = Color3[2]
console.log(colorName) // Displays 'Green' as its value is 2 above


// Any
var notSure: any = 4
notSure = "maybe a string instead"
notSure = false // okay, definitely a boolean

var notSure: any = 4
notSure.toFixed() // okay, toFixed exists (but the compiler doesn't check)

let prettySure: Object = 4
// prettySure.toFixed() // Error: Property 'toFixed' doesn't exist on type 'Object'.

let list_any: any[] = [1, true, "free"]
list_any[1] = 100
console.log(list_any) // [ 1, 100, 'free' ]


// Void
function warnUser(): void {
    alert("This is my warning message")
}

let unusable: void = undefined;



// Null and Undefined

// Not much else we can assign to these variables!
let u: undefined = undefined;
let n: null = null;


// Never
// Function returning never must have unreachable end point
function error(message: string): never {
    throw new Error(message);
}

// Inferred return type is never
function fail() {
    return error("Something failed");
}

// Function returning never must have unreachable end point
function infiniteLoop(): never {
    while (true) {
    }
}



// Type assertions
var someValue: any = "this is a string";
var strLength: number = (<string>someValue).length;

var someValue: any = "this is a string";
var strLength: number = (someValue as string).length;