Types in JavaScript

1. The variable is of no type, and the value (direct amount) only has the type.

The return value of 2.typeof has ' string ', ' number ', ' Undefined ', ' Boolean ', ' object '.

When you operate on a variable, 3.typeof is actually the type of the value that returns the variable.

4. A bug that has been there and may never be. The return value of typeof null is ' object '.

There are two cases where the 5.typeof return value is ' undefined '. One is undefined, unspecified, and the other is Undeclare, undeclared, in which case the browser returns an error that is not defined, and all many times it can be done with typeof a!== ' undefined ' to reduce the exception.

Types in JavaScript