Hash Tables & JavaScript Objects

const obj = {};
Object.defineProperty(obj, 'key', {
  value: 42,
  writable: false,
  enumerable: true,
  configurable: false
});

A temporary property
A mutable property
An immutable property
This code creates an immutable property because: 1) writable: false prevents value modification, 2) configurable: false prevents property deletion and descriptor changes, 3) enumerable: true allows property to appear in loops, 4) value: 42 sets the fixed property value, 5) Property cannot be changed or deleted once defined, 6) Attempts to modify will fail silently or throw in strict mode, 7) Common pattern for defining constants on objects, 8) Important for creating secure object properties.
A deletable property