CODEWITHSUNDEEP
reactjstypescript
Ayaz
Ayaz

Reputation: 2121

TypeScript - Argument of type 'String' is not assignable to parameter of type 'string'

I am trying to add extension method to String in typescript. Please help me to solve the below compile error.

I have added the below code in string-extensions.ts file in reactjs project.

declare global {  
    interface String {
        toNumber(): number;
    }
}  

String.prototype.toNumber = function() { return parseFloat(this);}

export {};

I am getting the error: Argument of type 'String' is not assignable to parameter of type 'string'. 'string' is a primitive, but 'String' is a wrapper object. Prefer using 'string' when possible. TS2345

I tried the below code on typescript compiler. It runs and display the output but it also gives the compiler error: enter image description here enter image description here

Upvotes: 1

Views: 16606

Answers (1)

choz
choz

Reputation: 17858

As the error mentions that String is a wrapper object by TS and that parseFloat accepts the first parameter as string.

As for workarounds, you can do one of the following;

String.prototype.toNumber = function() { return parseFloat(this.toString());}

// or
String.prototype.toNumber = function() { return parseFloat(this as string);}

Upvotes: 2

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