WebIDL

May 20, 2023

Web Interface Definition Language (WebIDL) is a language used to describe the interfaces of web APIs. WebIDL is a specification developed by the World Wide Web Consortium (W3C), specifically the Web Applications Working Group. The purpose of WebIDL is to define a syntax and semantics for describing interfaces that are exposed to the web, allowing them to be easily understood by both humans and machines.

Purpose and Usage

WebIDL provides a standardized way to define the interfaces of web-based APIs, which are used to implement various features of web applications. These APIs can include, among others, the Document Object Model (DOM), WebGL, Web Audio API, and WebRTC.

WebIDL defines a syntax for describing the properties, methods, and events of an interface, as well as for defining interfaces that inherit from other interfaces. This syntax is designed to be simple and easy to read, making it accessible to both developers and non-developers alike.

WebIDL also defines a set of rules for how interfaces can be used, including rules for inheritance, overloading of methods, and optional arguments. These rules help to ensure that APIs are consistent and predictable, and allow developers to write code that is more maintainable and less error-prone.

WebIDL is used by browser vendors, developers, and standards bodies to define, implement, and document web APIs. By providing a standardized way to describe web APIs, WebIDL helps to promote interoperability between different browsers and platforms. It also helps to ensure that web APIs are stable and reliable, and that they meet the needs of developers and end-users alike.

Syntax

WebIDL syntax is similar to that of object-oriented programming (OOP) languages, such as Java or C++. Interfaces are defined using the interface keyword, followed by the name of the interface and a set of curly braces that enclose the properties, methods, and events of the interface.

Example:

interface MyInterface {
  attribute DOMString myProperty;
  void myMethod();
  attribute EventHandler myEvent;
};

In this example, MyInterface is defined as an interface that has three members: a property called myProperty, a method called myMethod, and an event called myEvent. The attribute keyword is used to define properties and events, while the void keyword is used to define methods that do not return a value.

Inheritance

Interfaces in WebIDL can inherit from other interfaces using the extends keyword. For example:

interface MyInterface : ParentInterface {
  attribute DOMString myProperty;
  void myMethod();
  attribute EventHandler myEvent;
};

In this example, MyInterface inherits from ParentInterface, which means it will have access to all of the properties, methods, and events defined in ParentInterface.

Overloading

WebIDL allows methods to be overloaded, which means that multiple methods can have the same name but different parameter lists. For example:

interface MyInterface {
  void myMethod();
  void myMethod(DOMString arg1);
  void myMethod(DOMString arg1, unsigned long arg2);
};

In this example, myMethod is defined three times with different parameter lists. When a developer calls myMethod, the correct version of the method will be invoked based on the number and types of arguments passed.

Optional Arguments

WebIDL allows method arguments to be optional by using the optional keyword. For example:

interface MyInterface {
  void myMethod(DOMString arg1, optional unsigned long arg2);
};

In this example, arg2 is optional, which means that it can be omitted when calling myMethod. If arg2 is not provided, it will default to undefined.