Infer type when object coerced to string if toString explicitly defined #35945

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1. Aleksey Levenstein (levenleven)

   changed the title [-]Infer type when object coerced to string if `toString` explicitly defined[/-] [+]Infer type when object coerced to string if toString explicitly defined[/+] on Jan 1, 2020
2. Ryan Cavanaugh (RyanCavanaugh)

   added

   Awaiting More FeedbackThis means we'd like to hear from more people who would be helped by this featureThis means we'd like to hear from more people who would be helped by this feature

   SuggestionAn idea for TypeScriptAn idea for TypeScript

   on Jan 31, 2020
3. rihok commented on Aug 27, 2020

   

   Riho Kroll (rihok)

   on Aug 27, 2020

   More actions

   I think this would definitely be useful.

   As it stands today, TS doesn't really allow for explicit toString, which in some sense makes it incompatible with regular JS. Unless you give up pretty much all type safety for a given value. Adding { toString(): string } to your types essentially means you accept everything. I'm not sure if automatically accepting toString where string literal is expected would be a good idea, however a way to specific that explicit toString is accepted, would help with many different cases use-cases.
4. isometriq commented on Jun 15, 2021

   

   Daniel Lorenzo (isometriq)

   on Jun 15, 2021

   Last edited by isometriq

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   for this to work safely, would require to instruct the compiler with a type like string | { toString(): string }, or somehow a new conventional type like tostring ? serializable, stringprovider, etc...

   class ComplexObject {
     toString() {
       return 'serialized-value';
     }
   }
   
   type tostring = string | { toString(): string };
   
   function doSomething1(value: string | { toString(): string }) {;}
   function doSomething2(value: tostring) {;}
   
   const obj = new ComplexObject();
   doSomething1(obj);
   doSomething2(obj);