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Object.defineProperty is a method of the JavaScript Object constructor used to define a new property on an object or modify an existing one, returning the object itself. It offers fine-grained control over how a property behaves.

The method takes three arguments: the target object, a property name, and a descriptor object. The descriptor can define a data property by specifying value, writable, enumerable, and configurable; or an accessor property by providing get and set functions. Data properties hold a value, while accessor properties define behavior through getter and setter functions.

If attributes are omitted, their defaults apply. For data properties, writable, enumerable, and configurable default to false unless specified; value is set to the provided value or undefined. For accessor properties, get and set define the property’s behavior and must be functions; data attributes like value or writable are not used for accessors.

Common uses include creating properties with controlled visibility (non-enumerable), implementing read-only properties, defining lazy or computed values via getters, and polyfilling environments. It is also used to define properties with precise behavior during object construction or library initialization.

Caveats include that redefining a non-configurable property with incompatible descriptors throws a TypeError. Object.defineProperty can be combined with Object.defineProperties to define multiple properties at once. It is widely supported in modern JavaScript environments.

Example: Object.defineProperty(obj, 'id', { value: 123, writable: false, enumerable: true, configurable: false }); This creates a non-writable, enumerable, non-configurable data property.