An interface is a description of the actions that an object can do.

You might already be familiar with interfaces in other programming languages like C# and Java, or contracts in Swift.

Interfaces are not part of the ECMAScript. It is a level of abstraction supported by TypeScript to improve the type-checking process, and not converted to JavaScript code.

Here's an example of an interface describing generic Text component:

interface TextComponent {

    text: string;
    render(): void;


Now you can use the interface above to describe the requirement of having the text property that is a string and a render method:

class PlainTextComponent implements TextComponent {

    text: string;

    render() {
        console.log('rendering plain text component');


We are using implements keyword to wire class with a particular interface. It is not important in what order class members are defined as long as all properties and methods the interface requires are present and have required types.

Let's create another class that implements TextComponent interface partially:

class RichTextComponent implements TextComponent {
    text: string;

Upon compilation TypeScript will produce the following error:

error TS2420: Class 'RichTextComponent' incorrectly implements interface 'TextComponent'.
Property 'render' is missing in type 'RichTextComponent'.

You can use multiple interfaces delimited by a comma:

class RichTextComponent implements TextComponent, OnInit, OnDestroy {
    // ...

The example above shows a class that must implement three different interfaces to compile.