Can a TypeScript interface have default values?

To set default values for an interface in TypeScript, create an initializer function, which defines the default values for the type and use the spread syntax (…) to override the defaults with user-provided values.

What is default value of number in TypeScript?

In Javascript, the default value of an unassigned variable is undefined , as defined here. For example, the following typescript code: let a: string; console. log(a);

Does TypeScript support interface?

Typescript allows an interface to inherit from multiple interfaces. Use the extends keyword to implement inheritance among interfaces.

What is type interface in TypeScript?

TypeScript Interface Type TypeScript allows you to specifically type an object using an interface that can be reused by multiple objects. To create an interface, use the interface keyword followed by the interface name and the typed object.

How do you create an object with default values in TypeScript?

To set default value for an object parameter:

  1. Type the object as having one or more optional properties.
  2. Set default value for each of the optional properties.
  3. Alternatively, set the entire object as optional, by setting all its properties to optional.

Can we have an interface with optional and default properties in TypeScript?

We can define optional properties on an interface using? and read-only properties by using the readonly keyword in the property name. The TypeScript compiler also checks for excess properties on an object and gives an error if an object contains a property that is defined in the interface.

How do I declare a default value in TypeScript?

Use default parameter syntax parameter:=defaultValue if you want to set the default initialized value for the parameter. Default parameters are optional. To use the default initialized value of a parameter, you omit the argument when calling the function or pass the undefined into the function.

How do I pass a default value in TypeScript?

To set a default value for a function parameter, use an equal sign right after the parameter name, e.g. function multiply(num: number, by = 10) {} . If a value for the parameter is not provided, the argument will be replaced with the default value.

How do I initialize empty interface in TypeScript?

Use a type assertion to initialize a typed, empty object using an interface in TypeScript, e.g. const emp1 = {} as MyInterface . You can access or set any properties on the object, as long as they exist on the interface and are compatible with the corresponding types.

Can interface extend class TypeScript?

In TypeScript, interfaces can also extend classes, but only in a way that involves inheritance. When an interface extends a class, the interface includes all class members (public and private), but without the class’ implementations.

What’s the difference between a type and an interface?

Key Differences between TypeScript type vs interface Whereas interfaces are defined as a declaration of the only object type, which means the interfaces are restricted to only object type and do not support any other type for declaration. But we can say that interfaces have more capabilities than types in typescript.

Should I use interface or type?

Interface work better with objects and method objects, and types are better to work with functions, complex types, etc. You should not start to use one and delete the other.