CODEWITHSUNDEEP
interfaceargumentstypescriptdefault-value
Grofit
Grofit

Reputation: 18445

Typescript - Default parameters on class with interface

I have a scenario where I have an interface which has a method like so:

interface SomeInterface
{
   SomeMethod(arg1: string, arg2: string, arg3: boolean);
}

And a class like so:

class SomeImplementation implements SomeInterface
{
   public SomeMethod(arg1: string, arg2: string, arg3: boolean = true){...}
}

Now the problem is I cannot seem to tell the interface that the 3rd option should be optional or have a default value, as if I try to tell the interface there is a default value I get the error:

TS2174: Default arguments are not allowed in an overload parameter.

If I omit the default from the interface and invokes it like so:

var myObject = new SomeImplementation();
myObject.SomeMethod("foo", "bar");

It complains that the parameters do not match any override. So is there a way to be able to have default values for parameters and inherit from an interface, I dont mind if the interface has to have the value as default too as it is always going to be an optional argument.

Upvotes: 50

Views: 41578

Answers (1)

Ryan Cavanaugh
Ryan Cavanaugh

Reputation: 220964

You can define the parameter to be optional with ?:

interface SomeInterface {
     SomeMethod(arg1: string, arg2: string, arg3?: boolean);
}

Upvotes: 79

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