Number type learning notes in JavaScript

IEEE754 format is used to represent integer and floating point values.

Floating point value: This value must contain a decimal point, and there must be at least one number after the decimal point. Floating point values require twice the memory space as much as the integer value. The highest accuracy is 17 as a decimal, but its accuracy is far less than that of integers when performing arithmetic operations.

Various numerical types: decimal, octal (invalid in strict mode), hexadecimal

The first bit of the octal literal must be 0, followed by the octal number sequence (0~7). If the numeric value in the literal value is out of range, the leading 0 will be ignored and the subsequent numeric value will be parsed as a decimal number

 070//56079//79

The first two digits of the hexadecimal literal must be 0x followed by the hexadecimal digits (0~9 and A~F). The letters A~F can be sized or lowercase

 0xA//10

When performing arithmetic calculations, all values expressed in octal and hexadecimal will eventually be converted to decimal values

Value range:

If a value outside the javascript value range is obtained in the result of a calculation, then this value will be converted to a special Infinity value, which cannot participate in the next calculation because Infinity is a value that cannot participate in the calculation. If this number is positive, it is converted to Infinity (positive infinite), and if this number is negative, it is converted to -Infinity (negative infinite).

 -10/0//-Infinity10/0//Infinity

isInfinite() determines whether a number is finite.

 var result = Number.MAX_VALUE + Number.MAX_VALUEconsole.log(isFinity(result));//false

NaN

 console.log(NaN === NaN)//false0/0//NaN

isNaN: Receive a parameter, and will try to convert this value into a numeric value, returning a Boolean value

 console.log(isNaN('10'));//falseconsole.log(isNaN('bb'));//true

Numerical conversion

There are 3 functions that can convert non-numeric values into numeric values

Number(): Used for any numerical type.

1.null

 Number(null)//0undefinedNumber(undefined)//NaN

2. Boolean value

 Number(true)//1Number(false)//0

3. String

 Number('bb')//NaN, non-numeric character Number('123')//123, numeric character Number('')//0, empty string

4. Object

If it is an object, call the valueOf() method of the object, and then convert the returned value according to the above rules. If the result of the conversion is NaN, the object's toString() method is called, and the returned string value is converted again according to the previous rules.

5.parseInt()/parseFloat(): Used to convert a string to a numeric value.

parseInt(): start parsing from the first string until it is parsed to non-numeric characters. Two parameters can be accepted. The second parameter represents a different binary and is converted to a decimal number by default.

 parseInt('')//NaN, empty string parseInt(22.4)//22parseInt('12bu')//12parseInt('10',2)//2parseInt('10',8)//8parseFloat(): start parsing from the first string, the first decimal point is valid, ignore the leading 0 and can only be converted to decimal values. parseFloat('')//NaNparseFloat('090')//90parseFloat('2.3.4')//2.3

Summarize

• In addition to distinguishing between integer values and floating-point numbers, all numbers in JavaScript are identified by 64-bit floating-point values (IEEE 754).
• Just like the double type that java programmers are familiar with
• The value range is between ±1.7976931348623157 × 10 308 to ±5 × 10 −324

• Word:

  • Integer
    • Hexadecimal 0x
    • Octal 0
  • Floating point representation
  • Math class
    • method
      • pow // Seek power
      • round //round
      • ceil //Solid upwards
      • floor //Fill down
      • abs // Find the absolute value
      • max //maximum value
      • min //Minimum value
      • sqrt
      • log
      • exp
      • acos
      • asin
      • atan
      • atan2
      • random
      • sin
      • cos
    • constant
      • PI
      • E
      • LN2
      • LN10
      • LOG2E
      • LOG10E
      • PI
      • SQRT1_2
      • SQRT2
  • Unlimited value
    • Just infinity
      • Infinity //rw
      • Number.POSITIVE_INFINITY // r
      • 1/0
      • Number.MAX_VALUE + 1
    • Negative infinity
      • Number.NEGATIVE_INFINITY //rw
      • -Intifinty //r
      • -1/0
      • -Number.MAX_VALUE - 1
    • NaN
      • Not equal to any value including itself.
      • NaN //rw
      • Number.NaN //r
      • 0/0 //The calculation result is NaN
    • Zero
      • Number.MIN_VALUE/2
      • -Number.MIN_VALUE/2
      • -1/Infinity
      • -0

  • Rounding-error

 var x = .3 - .2 var y = .2 - .1 x == yx == .1 // => false .3 -.2 does not equal ./ y == .1 // => true .2 - .1 equals .1