#descriptors

Every object property in JS carries 4 flags under the hood (writable, enumerable, configurable, plus value or get/set). You rarely think about them - until something odd happens: an assignment doesn't change the value, delete doesn't remove the field, for...in skips the property. A note on what property descriptors are, how getters/setters work, and why Object.defineProperty has different defaults than an object literal.