[TypeScript] TypeScript Grammar - 01

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1.  Type Annotation

TypeScript uses colon ( : ) behind variables to annotate a type

const myMaxHamburger: number = 3;
const answer: string = "Yes I can";
const drinks: boolean = true;

You can code like variable: <type>

It is essential to write this annotation, so be careful to pass by this

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1_01.  Type Declaration_string

let str: string;
let red: string = 'Red';
let green: string = 'Green';
let myColor: string = `Do you like Color ${green}?`;

You can code like let <variable name>: <type>  

String type is just a letter that can't be calculated

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1_02.  Type Declaration_number

let num: number;
let integer: number = 6;
let float: number = 3.14;
let hex: number = NaN;

In Java, you can't use integers as float. But in Typescript, we can use them equally

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1_03.  Type Declaration_union type

let name: string | number = 'john';
let name: string | number = 123;
let name: string[] | number = ['test1', 'test2', 'test3'];

 

You can grammarly understand this as "You can use either A or B"

For example, we can call the name either string or number.

Therefore, it can be more flexible

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1_04.  Type Declaration_boolean

let isBool: boolean;
let isDone: boolean = false;

const size: number = 101;
const isHuge: boolean = size >= 99; // <- this area return as boolean type

 

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[TypeScript] TypeScript Grammar - 02