What is virtual-dom?

virtual-dom is a JavaScript library that implements the virtual DOM pattern for web applications. The idea behind it is straightforward: changing parts of a web page's DOM (the tree of elements the browser renders) is slow and error-prone when done manually. This library lets you describe what the page should look like as a plain JavaScript object tree, then automatically figures out the smallest set of real DOM changes needed to get there. The library has three core operations. First, you use a function called h (or the lower-level VNode objects directly) to build a virtual tree called a VTree, which describes the structure and properties of your UI. Second, when your data changes and you build a new VTree, the diff function compares the old tree to the new one and produces a compact list of changes. Third, the patch function takes that list and applies only those changes to the real DOM, leaving everything else untouched. This approach keeps rendering logic simple: you always describe the full desired state of the UI without tracking what changed since last time. The library handles the comparison and the minimal update. Input fields and scroll positions are not disturbed by changes that do not affect them, because unrelated parts of the DOM are left alone. The design was heavily inspired by the internal rendering approach used in Facebook's React framework, though it is a standalone module rather than part of any larger system. The virtual tree structure is designed to be efficient to build and read, avoiding the performance cost of working with actual DOM nodes until the patch step. The README includes a code example showing a counter that updates every second, demonstrating the full cycle of render, diff, and patch. Tool links at the bottom point to HTML-to-hyperscript converters that can help translate existing HTML into the hyperscript syntax the library uses.