The typeof operator returns the type of the argument. It’s useful when we want to process values of different types differently or just want to do a quick check.

A call to typeof x returns a string with the type name:

typeof undefined 
"undefined"

typeof 0 
"number"

typeof 10n
"bigint"

typeof true
"boolean"

typeof "foo"
"string"

typeof Symbol("id") 
"symbol"

typeof Math 
"object"

typeof null 
"object"

typeof alert 
"function"