Fetch API - Web APIs | MDN

Overview of the Fetch API

• Purpose: Provides a modern, powerful, and flexible interface for fetching network resources, serving as a replacement for XMLHttpRequest.
• Core Mechanism: Uses Request and Response objects, incorporating concepts like CORS and HTTP Origin header semantics.
• Primary Method: The fetch() method is a global function available in both Window and Worker contexts.
• Request Handling:
  • Takes a mandatory path argument and an optional init options object.
  • Returns a Promise that resolves to a Response object as soon as headers are received (even if the HTTP status indicates an error).
• Deferred Fetching: The fetchLater() API allows for requests to be sent after a delay or upon page navigation/closure.
• Key Interfaces:
  • Request and Response: Represent the network request and server response.
  • Headers: Allows querying and manipulation of request/response headers.
  • fetchLater() / DeferredRequestInit: Used for managing deferred network requests.
• Usage: While Request() and Response() constructors exist, they are typically generated automatically by API actions like fetch() or service worker events.