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Typescript for beginners: boolean

evaldasburlingis profile image Evaldas ・1 min read

Boolean is the data type that has two possible values. It is either true or false.

To do type checking on the variable we can write a statement as follows

const isTrue : boolean = true;

Step-by-step:

  • Define variable const isTrue
  • Add typescript type check : boolean
  • Define value true

To check whether function is returning boolean we can do it as fallows:

function isOlder(age : number) : boolean {
  return age >= 18 ? true : false;
}

isOlder(18) // true
isOlder(16) // false
isOlder(true) // error 'Argument of type boolean is not assignable to parameter of type number'

Step-by-step:

  • Define function function isOlder(argument : typecheck) : type to return {...}

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