fetching

Fetch refers to the act of retrieving data or resources from a source. In computing, it can mean retrieving a piece of data from memory, a cache, a device, or a network resource. In computer architecture, fetching is the first step in the instruction cycle where the processor reads an instruction from memory to be decoded and executed. In software development, fetching data commonly means requesting information from a remote server or API, or loading data from local storage.

The web environment popularized a specific programmatic pattern called the fetch operation. The fetch API in web browsers provides a modern, promise-based interface for making HTTP requests. It supports various methods such as GET and POST, headers, credentials, and modes like no-cors or cors. Responses can be consumed as text, JSON, Blob, or as a stream. Fetch operations are asynchronous and return a promise that resolves to a Response object. Note that fetch does not reject automatically on HTTP error statuses; the caller should check response.ok.

Security and performance considerations include cross-origin resource sharing (CORS), sanitization of inputs, and proper handling of credentials. Caching strategies, including HTTP cache headers and ETags, influence fetch latency. Streaming responses enable incremental processing of large payloads. Service workers can intercept fetch events to implement offline support and custom caching.

In data-focused applications, fetching is often paired with state management, loading indicators, and pagination or lazy loading to balance responsiveness with bandwidth. The term can also describe retrieving data in other layers, such as databases or file systems, where the term fetch is used informally to denote a read operation.