Web API

Reference: Client-side_web_APIs Introduction

Client-side JavaScript, in particular, has many APIs available to it — these are not part of the JavaScript language itself, rather they are built on top of the core JavaScript language. They generally fall into two categories:

Browser APIs are built into your web browser and are able to expose data from the browser and surrounding computer environment. For example, the Web Audio API provides JavaScript constructs for manipulating audio in the browser — taking an audio track, altering its volume, applying effects to it, etc. In the background, the browser is actually using some complex lower-level code (e.g. C++ or Rust) to do the actual audio processing. But again, this complexity is abstracted away from you by the API.

Third-party APIs are not built into the browser by default, and you generally have to retrieve their code and information from somewhere on the Web. For example, the Twitter API allows you to do things like displaying your latest tweets on your website.

• APIs for manipulating documents loaded into the browser. Example: DOM (Document Object Model) API. Find out more about these types of API in Manipulating documents..
• APIs that fetch data from the server to update small sections of a webpage are commonly used. The main API used for this is the Fetch API, although older code might still use the XMLHttpRequest API. Find out more about such APIs in Fetching data from the server.
• APIs for drawing and manipulating graphics are widely supported in browsers — the most popular ones are Canvas and WebGL, which allow you to programmatically update the pixel data contained in an HTML <canvas> element to create 2D and 3D scenes.
• Audio and Video APIs like HTMLMediaElement, the Web Audio API, and WebRTC
• Device APIs enable you to interact with device hardware: for example, accessing the device GPS to find the user's position using the Geolocation API.
• Client-side storage APIs enable you to store data on the client-side, so you can create an app that will save its state between page loads, and perhaps even work when the device is offline. There are several options available, e.g. simple name/value storage with the Web Storage API, and more complex database storage with the IndexedDB API.