Title rewritten as: Property does not exist on type 'Registration': Error: Property does not exist on type 'Registration'.ts(2339)

Question

I am developing using JavaScript and Typescript. I have the following function to check if an array has duplicates, but I'm getting an error and not sure how to fix it. Below are the errors and code excerpts.

Error: Property 'toLocaleLowerCase' does not exist on type 'Registration'. ts(2339)

Registration.ts

export interface Registration {
   address: string;
   comment?: string;
   fullname?: string;
  }

JS file

const nameAlreadyExist = (name: any): void => {
    const nameExist = filteredRegistrationName.value.findIndex((registrationName) => 
       registrationName.fullname.toLocaleLowerCase() === name.toLocaleLowerCase());
 
    nameExist != -1 ? (existNameError.value = true) : (existNameError.value = false);
   };

Any insights would be greatly appreciated. Thanks!

Answer 1

That's exactly what it means - it doesn't exist in your registeredtype. toLocaleLowerCase() only exists on the string type - so unless you can map the Registration type to the string, it won't work. I see that Registration.fullname is a string, but it's also optional - meaning it could be undefined, which could also throw an error.