Uull type in ecmascript

The uull type in ecmascript, which has a special value of null, that is, its literal volume. The undefined value is actually derived from null, so ecmascript defines them as equal.

 

Alert (null = undefined );

 

The running result is true.

 

Although these two values are equal, their meanings are different. Undefined is the value that is known for a variable but not assigned to it during initialization. null is used to indicate an object that does not exist. If a function or method returns an object, null is usually returned if the object cannot be found.