JavaScript notes and Summary (2-2) JavaScript variables

JS variable names can consist of _, number, letter, $, and cannot start with a number. A global variable of $ is defined in JQuery.

Declaring variables with var variable names, if not Var, will contaminate the global.

JS variable types include:

① Numeric type

② String Type

③ Boolean type (True,false)

④ Null type

var a = null

Object type not defined: null

var c = {Name:dee, age:29}//Object type

Console.log (C.name);

Console.log (c[' name ');

⑤ undefined type

var b = undefined;

Primitive types (numeric, string) are not defined: undefined

For example: Find a P tag on the DOM and return null (because the DOM is interpreted as a rendered object in the browser)

⑥ Array type (the array's keys increment from 0, and if a pair of key values is deleted, the index of the array is immediately rearranged)

var arr = [' A ', 1,true];

Console.log (arr);

Console.log (arr[2]);

JavaScript notes and Summary (2-2) JavaScript variables