JavaScript Advanced Programming Reading notes ~ Basic concepts

First, underfined and null

1. When declaring a variable using VAR, but not initializing it, the value of this variable is underfined

A 2.null value represents an empty object pointer, and if the defined variable is used in the future to hold the variable, it is better to initialize the variable to null instead of the other value

The 3.underfined value is derived from null so alert (null==underfined)//true

Two, Boolean type

1.Boolean only two literal literals can only be written as true, False and not written true,false

JavaScript Advanced Programming Reading notes ~ Basic concepts