JavaScript data types and data structures

Programming 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 or a 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:

var foo = 42;    // foo is now a number
foo     = ‘bar‘; // foo is now a string
foo     = true;  // foo is now a boolean

Data types

The latest ECMAScript standard defines eight data types:

• Seven data types that are primitives:
  • Boolean
  • Null
  • Undefined
  • Number
  • BigInt
  • String
  • Symbol
• and Object