How can you tell what type a value is, in JavaScript?

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JavaScript has a few built-in types, including numbers, strings, booleans, objects.

Using the typeof operator we can check what is the type of a value assigned to a variable.

For example:

typeof 'test'

Note that it’s not a function, it’s an operator, so parentheses are not required.

Using it, we will get a string back, returning one of the following values:

  • 'number'
  • 'string'
  • 'boolean'
  • 'undefined'
  • 'bigint'
  • 'symbol'
  • 'object'
  • 'function'

Note that there is no null type, and

typeof null

will return 'object'.

Arrays will return 'object' too:

typeof [1, 2, 3] //'object'

Functions are a special kind of objects, as we can add properties and methods to functions:

const talk = () => {}
talk.test = true

but they have their own value 'function' if we use the typeof operator.