1. Math object
1.1 Introduction
Math object is a mathematical object that provides mathematical calculations of data, such as: obtaining absolute values, rounding upwards, etc. There is no constructor, it cannot be initialized, only static properties and methods are provided.
1.2 Constructor
None: The Math object has no constructor and cannot be initialized. Only static properties and methods are provided.
1.3 Static properties
1.3.1: Constant e. Return the base number of natural logarithm: 2.718281828459045
1.3.2: Constant π. Return the value of Pi: 3.141592653589793
1.4 Static method
1.4.1 (value): Sine function
1.4.2 (value): Cosine function
1.4.3 (value): Tangent function
1.4.4 (value): Inverse sine function
1.4.5 (value): Inverse cosine function
1.4.6 (value): Arctangent function
1.4.7 (value): Returns absolute value
parameter:
①value {Number | NumberStr}: a string of numbers or pure numbers.
Return value:
{Number} Returns the absolute value of the parameter. If the parameter is not a number, return NaN.
Example:
('123'); // => 123: Pure numeric string
('-123'); // => 123
(123); // => 123
(-123); // => 123
('123a'); // => NaN: non-pure numeric string
1.4.8 (value): Rounding a number upward, not rounding
parameter:
①value {Number | NumberStr}: a string of numbers or pure numbers.
Return value:
{Number} Returns the rounded value. If the parameter is not a number, return NaN.
Example:
(2.7); // => 3
(2.3); // => 3:2.3 Round up and return 3
(-2.7); // => -2
(-2.3); // => -2
('2.7'); // => 3: Pure numeric string
('2.7a'); // => NaN: non-pure numeric string
1.4.9 (value): round downwards a number, not rounding
parameter:
①value {Number | NumberStr}: a string of numbers or pure numbers.
Return value:
{Number} Returns the rounded value. If the parameter is not a number, return NaN.
Example:
(2.7); // => 2
(2.3); // => 2
(-2.7); // => -3 : -2.7 Round down and return -3
(-2.3); // => -3
('2.7'); // => 2: Pure numeric string
('2.7a'); // => NaN: non-pure numeric string
1.4.10 (value1,value2...valueN): Returns the maximum value in the parameter
parameter:
①value1,value2......valueN {Number | NumberStr}: a string of numbers or pure numbers.
Return value:
{Number} Returns the maximum value. If a parameter is not a number, return NaN.
Example:
(1, 2, 3, 4, 5); // => 5
(1, 2, 3, 4, '5' ); // => 5
(1, 2, 3, 4, 'a'); // => NaN
1.4.11 (value1,value2...valueN): Returns the smallest value in the parameter
parameter:
①value1,value2......valueN {Number | NumberStr}: a string of numbers or pure numbers.
Return value:
{Number} Returns the maximum value. If a parameter is not a number, return NaN.
Example:
(1, 2, 3, 4, 5); // => 1
('1', 2, 3, 4, 5); // => 1
(1, 2, 3, 4, 'a'); // => NaN
1.4.12 (x,y): Return to the y power of x
parameter:
①x {Number | NumberStr}: a string of numbers or pure numbers.
②y {Number | NumberStr}: a string of numbers or pure numbers.
Return value:
{Number} Returns to the y power of x. If a parameter is not a number, return NaN.
Example:
(2, 3); // => 8:2 to the power of 3
(3, 2); // => 9:3 to the second power
('4', 2); // => 16:4 to the 2nd power
('2a', 2); // => NaN
1.4.13 (): Returns a pseudo-random number, greater than 0, less than 1.0
Parameters: None
Return value:
{Number} Returns a pseudo-random number, greater than 0, less than 1.0
Example:
(); // => 0.8982374747283757
(); // => 0.39617531932890415
(); // => 0.35413061641156673
(); // => 0.054441051790490746
1.4.14 (value): round it up
parameter:
①value {Number | NumberStr}: a string of numbers or pure numbers.
Return value:
{Integer} Returns the integer after the parameter is rounded. If the parameter is not a number, return NaN.
Example:
(2.5); // => 3
(2.4); // => 2
(-2.6); // => -3
(-2.5); // => -2 : -2.5 rounded to -2
(-2.4); // => -2
('2.7'); // => 3: Pure numeric string
('2.7a'); // => NaN: non-pure numeric string
1.4.15 (value): Returns the square root of the parameter
parameter:
①value {Number | NumberStr}: a string of numbers or pure numbers
Return value:
{Number} Returns the square root of the parameter
Example:
( (9) ); // => 3
( (16) ); // => 4
( ('25') ); // => 5
( ('a') ); // => NaN
2. Number object
2.1 Introduction
The Number object is a number object, which contains integers, floating point numbers, etc. in js.
2.2 Definition
var a = 1;
var b = 1.1;
2.3 Static properties
2.3.1 Number.MAX_VALUE: represents the largest number in JS, about 1.79e+308
2.3.2 Number.MIN_VALUE: represents the smallest number in JS, about 5e-324
2.3.3: Returns NaN, indicating a non-numeric value, which is different from any other number, including NaN itself. The judgment should be made using ().
2.3.4 Number.NEGATIVE_INFINITY: Returns -Infinity, indicating negative infinity.
2.3.5 Number.POSITIVE_INFINITY : Returns Infinity, indicating that positive infinity is infinity. If the calculated value is greater than Number.MAX_VALUE, it returns Infinity.
2.4 Static method
2.4.1 (value): determine whether the parameter is an integer
parameter:
①value {Number}: number
Return value:
{Boolean} Returns whether the parameter is an integer. A pure integer string also returns false.
Example:
(1); // => true
(1.1); // => false
('1'); // => false : A pure integer string also returns false
('1.1'); // => false
('a'); // => false : Non-string returns false
2.4.2 (value): determine whether the parameter is NaN
parameter:
①value {Object}: any type
Return value:
{Boolean} Returns whether the parameter is NaN.
Example:
(NaN); // => true
('NaN'); // => false :'NaN' string, not NaN
(1); // => false
('1'); // => false
2.4.3 (value): Convert parameters to floating point numbers
parameter:
①value {Number | NumberStr}: a string of numbers or pure numbers
Return value:
{Integer | Float} Returns integer or floating point value
Example:
(1); // => 1: Integer or return integer
(1.1); // => 1.1
('1aaa'); // => 1: The string is preceded by a number, only the number is returned
('1.1aaa'); // => 1.1
('a1'); // => NaN: Non-starting number, return NaN
('a'); // => NaN
2.4.4 (value): Convert parameters to integers
parameter:
①value {Number | NumberStr}: a string of numbers or pure numbers
Return value:
{Integer} Returns integer value
Example:
(1); // => 1
(1.1); // => 1: Floating point number returns integer
('1aaa'); // => 1: The string is preceded by a number, only the number is returned
('1.1aaa'); // => 1
('a1'); // => NaN: Non-starting number, return NaN
('a'); // => NaN
2.5 Example method
2.5.1 toExponential(value): convert a number to exponential type, and the parameter represents the number of digits after the decimal point
parameter:
①value {Number}: represents the number of digits after the decimal point
Return value:
{String} Returns the converted exponential type string
Example:
(123456789).toExponential(2); // => 1.23e+8: 2 decimal places
(123456789).toExponential(5); // => 1.23457e+8: 5 decimal places
(123456789).toExponential(10); // => 1.2345678900e+8: 10 decimal places, and 0 is used to fill in the number of insufficient digits
2.5.2 toFixed(value): Convert a number to a string with a specified decimal number. If no parameters are passed, there are no decimal places. Return value is rounded
parameter:
①value {Number}: represents the number of digits after the decimal point
Return value:
{String} Returns the converted string; not enough decimal places to be filled with 0; return value is rounded value
Example:
((1).toFixed(2)); // => 1.00
((1.2).toFixed(2)); // => 1.20: The number of insufficient digits, fill with 0
((1.277).toFixed(2)); // => 1.28: Rounding was performed
2.5.3 toString(): Use the specified binary to convert a number into a string. No parameters are passed in, the default is decimal.
parameter:
①value {Number} : represents the number of the binary, with value range: 2 to 36
Return value:
{String} Converts a later string
Example:
(10).toString(); // => 10: Decimal default
(10).toString(2); // => 1010: Binary
(10).toString(10); // => 10: decimal
(10).toString(16); // => a: hexadecimal
2.6 Application scenarios
2.6.1 Addition, subtraction, multiplication and division exceptions of floating point numbers
Note: If two floating-point numbers in Js are added, subtracted, multiplied and divided, they will return the abnormal value, such as: 0.2+0.7, and return 0.899999999999999. You can use the toFixed() method to specify decimal places.
Example:
(0.2 + 0.7); // => 0.8999999999999999
(0.7 - 0.5); // => 0.19999999999999996
(3.03 * 10); // => 30.299999999999997
// Use the toFixed() method
( (0.2 + 0.7).toFixed(2) ); // => 0.90
( (0.7 - 0.5).toFixed(2) ); // => 0.20
( (3.03 * 10).toFixed(2) ); // => 30.30
2.6.2 Subtraction operation
Note: When performing subtraction operations in Js, the previous and subsequent values will be converted into numeric values before performing operations. If the conversion fails, return NaN.
Example:
('1' - 0); // => 1: Subtract 0 from a pure numeric string, which can be quickly converted to a Nubmer object
( ('1' - 0).toFixed(2) ); // => 1.00: Call the instance method after quickly converting to a Nubmer object
('1' - 'a'); // => NaN: One party cannot convert to a Nubmer object