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TypeScript - Basic Data Types

[Updated: Oct 28, 2018, Created: Aug 26, 2018]

Following is a quick walk through of TypeScript basic data types.

Data Type Description Examples
boolean
logical values: true or false.
let active: boolean = false;
let enabled: boolean = true;
number
floating point values. (decimal, hexadecimal, binary, octal)
let x: number = 5;
let y: number = 1.5;
let z: number = Math.PI;
string
textual data
let message: string = "hello";
let x: number = 5;
let fullMessage: String  = `message number: ${x},  ${message}`; 
console.log(fullMessage);
message number: 5,  hello 
Arrays
Either [] or <> is used.
let evens: Array<number> = [2, 4, 6];
let odds: number[] = [1,3,5];
Tuple
Array of different types
let myData: [string, number] = ["hi", 5]; //tuple
myData.forEach((value, index) => {
console.log(`val: ${value}, index: ${index} type: ${typeof value}`);         
});
val: hi, index: 0 type: string
val: 5, index: 1 type: number
enum
Enumerated constants
enum Food {Pasta, Rice};     
console.log(Food.Pasta);
console.log(Food.Rice);

console.log(Food[1]);

let x: Food = Food.Rice;
console.log(x);
0
1
Pasta
1

Manual numbering:

enum Food {Pasta=3, Rice=5};  
console.log(Food.Pasta);
console.log(Food.Rice);
3
5

This is also possible:

enum Food {Pasta='one', Rice='two'};
console.log(Food.Pasta);
console.log(Food.Rice);
one
two
Any
assignable to any type
let x : any = "a string";
console.log(typeof x)
x = 2;
console.log(typeof x)
x = true;
console.log(typeof x)
string
number
boolean
void
return type of a function which returns nothing
function showSquare(x: number): void{
    console.log(x*x);
}

showSquare(6);
36
Object
type of an object instance

TypeScript support class syntax similar to ES6 class:

class Shape{
    draw(){
        console.log("drawing shape");
    }
}

let shapeInstance: Shape = new Shape();
shapeInstance.draw();
drawing shape 
null
type of null literal
let x: null = null;
//other types can be assigned to null
let y: string = null;
undefined
type of undefined literal
let x: undefined = undefined;
//other types can be assigned to undefined
let y: string = undefined;
never
return type of a function that never returns
function doSomething(message: string): never {
  throw new Error(message);
}

See Also