Data types and naming conventions in JavaScript

There are 7 types of data:

undefined(Not defined)

null(empty),

boolean(Boolean type)

stringString

symbol(symbol),

numberDigital

objectObject

Naming rules

VariableThe name of (a variable) can be a number, a letter, $ or a _ composition, but not a space or a number headed.

Attention:

When a variable in JavaScript is declared, the inside of the program gives it an initial value undefined . When you perform an operation on a variable that is a value undefined , the result will be NaN , "not a number NaN ". When you use a non 定义 -variable to do a string connection operation, it will output truthfully "undefined" .

All variables in JavaScript are case-sensitive. This means that you have to treat the uppercase and lowercase letters differently.

"your name"is called a string . A string is a series of 0 or more characters wrapped in single or double quotation marks.

In JavaScript, you can \ escape quotation marks by using a backslash () in front of the quotation marks.

Data types and naming conventions in JavaScript