Interfaces in TypeScript are a way to define the shape of an object. They are similar to type aliases, but with some differences.
Creating an interface
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| interface Person {
name: string;
age: number;
}
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Creating an interface with optional properties
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| interface Person {
name: string;
age?: number;
}
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In the above example, the age property is optional.
Creating an interface with readonly properties
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| interface Person {
readonly name: string;
readonly age: number;
}
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In the above example, the name and age properties are readonly. This means that they cannot be changed after they are created.
Creating an interface with methods
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| interface Person {
name: string;
age: number;
sayHello(): void;
}
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In the above example, the sayHello method takes no arguments and returns nothing.
Creating an interface with a method that takes arguments
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| interface Person {
name: string;
age: number;
sayHello(name: string): void;
}
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In the above example, the sayHello method takes a name argument and returns nothing.
Using an interface
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| let person: Person = {
name: "John",
age: 30,
};
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- using an interface that has a method
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| let person: Person = {
name: "John",
age: 30,
sayHello(name: string): void {
console.log(`Hello, ${name}!`);
},
};
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Extending an interface
In TypeScript, you can extend an interface by using the extends keyword. This allows you to add new properties to an existing interface.
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| interface Person {
name: string;
age: number;
}
interface Employee extends Person {
salary: number;
}
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Reopening an interface
In TypeScript, you can reopen an interface by using the declare keyword. This allows you to add new properties to an existing interface.
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| interface Person {
name: string;
age: number;
}
declare interface Person {
salary: number;
}
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