CODEWITHSUNDEEP
javascriptangulartypescript
user9869932
user9869932

Reputation: 7337

Is there a way to get the type of an uninitialised variable in Typescript?

I have a variable a declared with type string, but uninitialised. Is there a way to get the string type instead of an undefined?

> let a:string;
undefined
> console.log(typeof a);
undefined

Upvotes: 0

Views: 248

Answers (2)

user9869932
user9869932

Reputation: 7337

As there is no way to get the type at runtime; and based on @deceze's comment (save the metadata separately)

In case it helps someone this workaround does the job. It does not use Reflect decorators

> class C {
  constructor(
     public var1?:string, 
     public var2?:string, 
     public var3?:number
  ) {}
  typeof(v) {
     switch (v) {
     case 'var1':
     case 'var2':
       return 'string';
     case 'var3':
       return 'number';
     }
   }
}
> let c = new C();
> console.log(Object.keys(c).map( 
     a => {
       console.log( ' Var: ' + a + 
                    ' - Type: ' + c.typeof(`${a}`) )
     })
  );

 Var: var1 - Type: string
 Var: var2 - Type: string
 Var: var3 - Type: number
[ undefined, undefined, undefined ]

Typescript Playground

Upvotes: 0

Andrei
Andrei

Reputation: 12021

yes, there is a way to get types metadata in typescript, but you would have to activate reflect metadata option in typescript compiler config and import reflect metadata polyfill, which will increase you bundle size.

look here to find more suitable example of accessing typescript types.

Upvotes: 2

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