The undefined type is a primitive type that has one value undefined . By default, when a variable is declared but not initialized, it is assigned the value undefined . Since counter hasn’t been initialized, it is assigned the value undefined . The type of counter is also undefined .
How do you know if a variable is undefined?
To check if a variable is undefined, you can use comparison operators — the equality operator == or strict equality operator === . If you declare a variable but not assign a value, it will return undefined automatically. Thus, if you try to display the value of such variable, the word “undefined” will be displayed.
Is undefined or null JS?
What is the datatype of undefined?
- Using typeof operator. The recommended solution is to use the typeof operator to determine the type of operand.
- Using Object.prototype.toString.call() function.
- Using Lodash/Underscore Library.
- Using jQuery.
Falsy equality using ==.
null is used to explicitly define “nothing”. For example,var foo = null;