JavaScript Advanced Programming Learning notes (1)

Basic concepts

1 Data type undefined type

The undefined type uses only one value, which is the special undefined. When declaring a variable with VAR but not initializing it, the variable is undefined, for example:

VAR message;

Alert (message = = undefined);???? True

?

Boolean type

The Boolean type has only two values of true and false;

Translation rules that are extremely relevant for various data types

data type	to a value of true	value converted to false
Boolean	True	false
String	Any non-null character	" (empty string)
number	Any non-0 numeric value (including infinity)	0 and Nan
Object	Any object	null
Undefined	N/A	Undefined

?

Number Type

NaN:

JavaScript Advanced Programming Learning notes (1)