JavaScript data types and data structures

Programing languages all have built-in data structures, but these often differ from one language to another. This article attempts to list the built-in data structures available in JavaScript and what properties they have. These can be used to build other data structures. Wherever possible, comparisons with other languages are drawn.

Dynamic typing

JavaScript is a loosely typed and dynamic language. Variables in JavaScript are not directly associated with any particular value type, and any variable can be assigned(and re-assigned) values of all types.

Data and Structure types

The latest ECMAScript standard defines nine types:

• Six Data Types that are primitives, checked by typeof operator:
  • undefined: typeof instance === "undefined"
  • Boolean: typeof instance === "boolean"
  • Number: typeof instance === "number"
  • String: typeof instance === "string"
  • BigInt: typeof instance === "bigint"
  • Symbol: typeof instance === "symbol"
• Structural Types:
  • Object: typeof instance === "object". Special non-data but Structural type for any constructed object instance also used as data structures: new Object, new , new Map, new Set, new WeakMap, new WeakSet, new Date and almost everything made with new keyword.
  • Function: a non-data structure, though it also answers for typeof operator: `typeof instance === "function"'. This is merely a special shorthand for Functions, through every Function constructor is derived from Object constructor.
• Structural Root Primitive:
  • null: typeof instance === "object". Special primitives type having additional usage for its value: if object is not inherited, the null is shown.