[JS] Lesson 7: Numbers

1.number reference type

1.1 Number as constructor

var num=new Number(10);

1.2 Number as a tool function


[Run result]

Properties on 1.3 Number constructor

console.log(Number.POSITIVE_INFINITY);//plus infinity
console.log(Number.NEGATIVE_INFINITY);//negative infinity
console.log(Number.NaN);//Not a number
console.log(Number.MAX_VALUE);//Maximum number in JS
console.log(Number.MIN_VALUE);//Minimum in JS
console.log(Number.MAX_SAFE_INTEGER);//The largest integer that can be accurately represented in JS
console.log(Number.MIN_SAFE_INTEGER);//The smallest integer that can be accurately represented in JS

[Run result]

Method on 1.4 Number constructor

  1. Number.isFinite(number) detects whether a number is infinite
console.log(Number.isFinite(0));  //true
console.log(Number.isFinite(Number.POSITIVE_INFINITY));  //false
console.log(Number.isFinite(Number.NaN));  //false
  1. Number.isInteger(number) detects whether a number is an integer
console.log(Number.isInteger(0.1));  //false
console.log(Number.isInteger(Infinity));  //false
console.log(Number.isInteger('1'));  //false
console.log(Number.isInteger(1));  //true
console.log(Number.isInteger(1.0));  //true
  1. Number.isSafeInteger(number) detects whether a number is a safe integer
  2. Number.isNaN(number) detects whether a number is an integer
console.log(Number.isNaN(0.1));  //false
console.log(Number.isNaN(NaN));  //true
console.log(Number.isNaN(0/0));  //true
console.log(Number.isNaN('string'));  //false
console.log(Number.isNaN(1/'abc'));  //true
  1. Number.parseInt(string, radix)
    String:Converted string
    radix: binary type
    Return value: converted integer
    Equivalent to the global parseInt(string, radix) method
console.log(parseInt("1")); //1
console.log(parseInt("1.1")); //1
console.log(parseInt("1a2.23")); //1
console.log(parseInt("abc")); //NaN
  1. Number.parseFloat(string)
    Equivalent to the global parseFloat(string) method
console.log(Number.parseFloat('0.1'));  //0.1
console.log(Number.parseFloat('12'));  //12
console.log(Number.parseFloat('12.3abc'));  //12.3

Method on 1.5 Number prototype chain

  1. number.prototype.toFixed(fractionDigits)
    Function: Keep the number of decimal places in the specified number of digits
    FractiononDigits: Number of digits after the decimal point
    Return value: fixed-point formatted string
var num=10.005;
num.toFixed(2); //10.01
100.01.toFixed(2);  //100.01
(100).toFixed(2);   //100.00 Integer bracketed
  1. number.prototype.toExponential(franctionDigits)
    Function: Converts a numeric value to an exponential form and returns a string
    FractiononDigits: Number of digits after the decimal point
    Return value: String in exponential form
(1).toExponential(2);    //1.00e+0 
(10000).toExponential(1);      //1.0e+4
  1. number.prototype.toPrecision(precision)
    Function: Returns a string representation of the value in the specified number of digits
    Precision: number of precision digits
    Return value: The string represented by the specified number of bits
(1.123).toPrecision();        //1.123
(1.123).toPrecision(2);       //1.1
(1.123).toPrecision(5);       //1.1230
(1.523).toPrecision(1);        //2
(1234.5).toPrecision(2);      //1.2e+3
  1. number.prototype.toString([radix])
    Function: Convert numeric values to strings
    radix: converted to decimal, default is 10
    Return value: String
console.log((10).toString());     //10
console.log((10).toString(2));    //1010
console.log((10).toString(8));    //12
console.log((10).toString(10));    //10
console.log((10).toString(16));     //a

2.Math Objects

1. Properties of Math objects

2. Methods of Math objects

  1. Math.abs(x)
    Return Number Type
Math.abs(-1);   //1
  1. Math.round(x)
    Function: Round the number x and return a number
Math.round(1.5);    //2
Math.round(1.4);   //1
  1. Math.ceil(x)
    Function: Rounding up
Math.ceil(1.1);  //2
  1. Math.floor(x)
    Function: Round down
Math.ceil(1.9);  //1
  1. Math.max(...)
  2. Math.min(...)
  3. Math.random()
    Function: Returns a random number in the range [0,1]
    No parameters
  4. ...
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Added by onepixel on Sat, 11 Jan 2020 05:44:34 +0200