“Emptiness” in javascript sometimes makes me scratch my head. Especially when checking for emptiness. Think I’m crazy? Ask your fellow developers to explain the difference between null + undefined.

What does the MDN say about NULL?

Null: The value null represents the intentional absence of any object value. It is one of JavaScript’s primitive values and is treated as falsy for boolean operations.

typeof null          // "object" (not "null" for legacy reasons)
typeof undefined     // "undefined"
null === undefined   // false
null  == undefined   // true
null === null        // true
null == null         // true
!null                // true
isNaN(1 + null)      // false
isNaN(1 + undefined) // true

What does the MDN say about Undefined?

Undefined: The global undefined property represents the primitive value undefined. It is one of JavaScript’s primitive types. A variable that has not been assigned a value is of type undefined. A method or statement also returns undefined if the variable that is being evaluated does not have an assigned value. A function returns undefined if a value was not returned.

How about a silly… but really easy to understand image. I found this on stack overflow.

Photo by Izz R on Unsplash