js basics-data types

type of data

Divided into two major types

1. Basic data types (simple data types)

• Number
• String
• Boolean
• Undefined 空
• null empty

2. Complex data type (address data type/reference data type)
   • Object
   • Function

Number

• All decimal numbers
• All floating point numbers (decimals)
• Numbers in other bases
  • Hexadecimal, starting with 0x
  • Octal, starting with 0
  • Binary, starting with 0b
• Scientific notation
  • Larger numbers are expressed in scientific notation
  • 2e5 2 * 10 to the 5th power
• NaN
  • Not a Number: Not a Number

String

• In JS, everything wrapped with quotation marks (double quotation marks, single quotation marks, back quotation marks) is a string

   var s1 = 'hello world' // 11 个字符组成
      console.log(s1)
        // 不是数字 123, 是 1 2 3 三个字符连接在一起
      var s2 = '123'
      console.log(s2)
      var n1 = 123
      console.log(n1)
  

• Represents a piece of text content, which is the content connected character by character

  • ‘hello’

  • “hello”

  • `hello`
    

• When you write only numbers in a string, it is not a numeric type.

• In the string, spaces are occupied

Boolean

• In JS, Boolean has only two values

  • true means true, and it is 1 when stored in the computer
  • false means false, it is 0 when stored in the computer

• What's the meaning in the calculation process

  • Mainly used for judgment

  • example

    ​ a> b If you get true, it means that the expression is true

    ​ a <b If you get false, it means that the expression is false

air

• Undefined 空
  • There should be a value here, but there is no, it is undefined
• Null
  • There is a value here, there is a null value