The difference between null and undefined

Null indicates that an object is defined with a value of " null ";

Undefined indicates that this value does not exist.

//

typeof undefined

"Undefined"

Undefined: is a primitive value that represents " none " or " missing value ", thatis, there should be a value here, but it is not yet defined. Undefined is returned when attempting to read;

For example, when a variable is declared but not assigned, it is equal to undefined.

typeof null

"Object"

Null: is an object ( empty object , without any properties and methods );

For example, as an argument to a function, the argument to that function is not an object;

Note: When validating null , be sure to use = = = , because = = cannot be null and undefined separately

The difference between null and undefined