JavaScript variables and data types

JavaScript is no stranger, so are JavaScript variables and data types deep enough?

variable

1, declare variables before assigning values

var width;
width = 9;

var: Is the keyword used to declare variables

width: Assigns a value to the variable name

2, declare and assign variables at the same time

var catName= "小明";
var x, y, z = 10;

3, do not declare direct assignment (rarely used)

width = 5;

Here variables can be used directly without declaration, but more error-prone, not easy to find and exclude errors, not recommended for everyone to use.

data type

1、undefined

Example: var width

The variable width has no initial value and is assigned a value of undefined

2、null

Represents an empty value equal to undefined

3、number

Var num=23 // This is an integer

Var num=23.0 // This is the floating point

4、Boolean

true and false but JS resolves to 1 or 0

5、String

Text enclosed in single or double quotes

var string = "This is a string"

That's all you need to do with JavaScript variables and data types.