1+ // Path: src/01-intro/08-typescript.ts
2+ 3+ let myName = 'Packt' ;
4+ // myName = 10; // commented to avoid error
5+ 6+ /* Type inference */
7+ let age = 20 ; // number
8+ let existsFlag = true ; // boolean
9+ let language = 'JavaScript' ; // string
10+ 11+ let favoriteLanguage : string ;
12+ let langs = [ 'JavaScript' , 'Ruby' , 'Python' ] ;
13+ favoriteLanguage = langs [ 0 ] ;
14+ 15+ /* Interfaces as type */
16+ interface Person {
17+ name : string ;
18+ age : number ;
19+ }
20+ 21+ function printName ( person : Person ) {
22+ console . log ( person . name ) ;
23+ }
24+ 25+ const john = { name : 'John' , age : 21 } ;
26+ const mary = { name : 'Mary' , age : 21 , phone : '123-45678' } ;
27+ printName ( john ) ;
28+ printName ( mary ) ;
29+ 30+ /* Interfaces as OO */
31+ interface Comparable < T > {
32+ compareTo ( b : T ) : number ;
33+ }
34+ 35+ class MyObject implements Comparable < MyObject > {
36+ age : number ;
37+ 38+ constructor ( age : number ) {
39+ this . age = age ;
40+ }
41+ 42+ compareTo ( b : MyObject ) : number {
43+ if ( this . age === b . age ) {
44+ return 0 ;
45+ }
46+ return this . age > b . age ? 1 : - 1 ;
47+ }
48+ }
49+ 50+ /* Enums */
51+ enum Compare {
52+ LESS_THAN = - 1 ,
53+ BIGGER_THAN = 1 ,
54+ EQUALS = 0
55+ }
56+ 57+ function compareTo ( a : MyObject , b : MyObject ) : number {
58+ if ( a . age === b . age ) {
59+ return Compare . EQUALS ;
60+ }
61+ return a . age > b . age ? Compare . BIGGER_THAN : Compare . LESS_THAN ;
62+ }
63+ 64+ /* Type aliases */
65+ type UserID = string ;
66+ type User = {
67+ id : UserID ;
68+ name : string ;
69+ }
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