Typescript default value of parent interface property

Question

interface Iparent {
  a: string
}
interface Ichild extends parent {
a: '';
}
const x: child = {}

This throws a compiler error when using child How to provide a default value for a in child interface?

Edit:

Class parent actually looks like this:

class parent extends React.Component<Iparent> {}

class child extends React.Component<Ichild> {}

parent class should have a prop but child class should just have a default value for it i.e. ''

Leszek Mazur · Accepted Answer · 2020-12-12 19:43:42Z

1

There are a few mistakes:

a: '' not do default value, it means that a can be only '' it is like animal: 'dog' | 'cat' may be only 'dog' or 'cat' value.
Interfaces have no default values - they are used like less specified types. If you want have default value you should use class child:

class child implements parent{
    a = '';
}
const x: child = new child();

answered Dec 12, 2020 at 19:43

Leszek Mazur

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