The attribute 'fit' within the Button type cannot be reassigned to the identical attribute in the base type 'IButton'. The string type cannot be reassigned to the Fit type

In my coding project, I have a Button class that implements the IButton interface.

class Button implements IButton {
   public fit = 'medium';
}
declare type Fit = 'small' | 'medium' | 'large';

export interface IButton {
  fit: Fit;
}

Despite setting 'medium' as the default value for the fit property in the Button class, TypeScript throws an error indicating that it is not assignable to type Fit.

Property 'fit' in type 'Button' is not assignable to the same property in base type 'IButton'.
Type 'string' is not assignable to type 'Fit'.

Is there an alternative approach to achieve this functionality?

Answer №1

If you define the variable as public size = 'large', TypeScript will automatically determine the type of size to be string. However, this may not align with the expected type in the interface IItems's property size.

To address this issue, consider the following solutions:

  1. Specify the variable as readonly
public readonly size = 'large'
  1. Utilize as const or as Size
public size = 'large' as Size
//public size = 'large' as const
  1. Manually indicate the accurate type
public size: Size = 'large'

Note: Only using as Fit or the third option will enable modifications to the value of size at runtime.

Answer №2

To export the Enum Fit, you can implement it in the following way:

class Button implements IButton {
   public fitSize = 'medium' as SizeFit;
}

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