Objects

JavaScript Property Descriptors with Object.defineProperty

Most JavaScript properties are created with assignment or object literals. That is usually the right choice, but it hides several controls that every property carries: whether the property can be assigned, whether common enumeration APIs expose it, and whether its definition can later be changed. Property descriptors make those controls explicit. They are useful for library APIs, metadata, computed properties, compatibility layers, and cases where ordinary assignment exposes more behavior than intended.