Principles of Two-Way Data Binding in Vue

Two-way data binding in MVVM consists of two main processes: when data changes, the view updates; when the view changes (e.g., user input), the data updates.

Vue achieves data binding by redefining object property accessors with Object.defineProperty, intercepting get and set operations to make data reactive.

The core components are:

Observer : a listener that hijacks all object properties, detects changes, and notifies a dependency manager.

Dep : a message broker that collects all Watcher subscribers for a property.

Watcher : a subscriber that receives change notifications from Dep and executes update functions to refresh the view.

Compile : a directive parser that scans DOM nodes, initializes data, creates corresponding watchers, and binds templates or functions to the view.

The flow can be visualized as: data → Observer → Dep → Watcher → view update, and vice‑versa for view → model.

In Vue's source code, the implementation is split into several files:

Observer.js : defines the observer that uses Object.defineProperty to monitor property changes.

Watcher.js : defines the watcher that reacts to observed changes and updates the DOM.

Compile.js : parses template directives, creates watchers, and binds data to the view.

Mvvm.js : orchestrates the overall MVVM initialization, linking the model, view, and observers together.

Overall, the article provides a conceptual diagram and pseudo‑code illustrating how Vue's data binding mechanism works under the hood.