JS foundation -- math

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What is? Math object

Math Object allows you to perform mathematical tasks .
Math Not a constructor .Math All attributes of / Methods can be used Math Call... As an object , Without creating it ：

Math Object properties

attribute	describe
E	Returns the Euler number （ about 2.718）.
LN2	return 2 The natural logarithm of （ about 0.693）.
LN10	return 10 The natural logarithm of （ about 2.302）.
LOG2E	return E The to 2 Log base （ about 1.442）.
LOG10E	return E The to 10 Log base （ about 0.434）.
PI	return PI（ about 3.14）.
SQRT1_2	return 1/2 The square root of （ about 0.707）.
SQRT2	return 2 The square root of （ about 1.414）.

Math Object methods

attribute	describe
abs(x)	return x The absolute value of .
acos(x)	return x The arccosine of , In radians .
acosh(x)	return x Hyperbolic arccosine of .
asin(x)	return x The arcsine of , In radians .
asinh(x)	return x Hyperbolic arcsine value of .
atan(x)	return x The arctangent of , The value returned is -PI/2 To PI/2 The radian value between .
atan2(y, x)	Returns the arctangent of its parameter quotient .
atanh(x)	return x Hyperbolic arctangent of .
cbrt(x)	return x The third root of .
ceil(x)	return x, Round up to the nearest integer .
clz32(x)	return x Of 32 The number of leading zeros in a bit binary representation .
cos(x)	return x Cosine of （x In radians ）.
cosh(x)	return x The hyperbolic cosine value of .
exp(x)	return Ex Value .
expm1(x)	return Ex subtract 1 Value .
floor(x)	return x, Round down to the nearest integer .
fround(x)	Returns the closest of the numbers （32 Bit single precision ） Floating point means .
log(x)	return x The natural logarithm of .
log10(x)	return x The to 10 Log base .
log1p(x)	return 1 + x The natural logarithm of .
log2(x)	return x The to 2 Log base .
max(x, y, z, …, n)	Return the highest number .
min(x, y, z, …, n)	Returns the number with the smallest value .
pow(x, y)	return x Of y Power value .
random()	return 0 To 1 Random number between .
round(x)	take x Round to the nearest integer .
sign(x)	Returns the sign of a number （ Check that it is a positive number 、 Negative or zero ）.
sin(x)	return x The sine of （x In radians ）.
sinh(x)	return x The hyperbolic sine of .
sqrt(x)	return x The square root of .
tan(x)	Returns the tangent of the angle .
tanh(x)	Returns the hyperbolic tangent of a number .
trunc(x)	Return to digital (x) The integral part of .

Several commonly used method cases

ceil(x) Round up logarithm .
floor(x) The logarithm is rounded down .
round(x) Round a number to the nearest whole number .

			var a=66.18
			console.log(Math.ceil(a))
			console.log(Math.floor(a))
			console.log(Math.round(a))

cos(x) Returns the cosine of a number
sin(x) Returns the sine of a number

// return 90 Sine value of degree 
			var deg=Math.PI/180  // representative 1 Degrees , Again JS The unit of middle angle is Math.PI/180 To express 
			var re=Math.sin(90*deg)
			console.log(re)

max(x,y) return x and y The highest value in .
min(x,y) return x and y The lowest of .
pow(x,y) return x Of y The next power .
sqrt(x) Returns the square root of a number .

random() Method to return from 0（ contain ） To 1（ Not included ） The random number .

			var re=Math.random()// Pseudo random number 	[0,1)
			console.log(re*10)//[0,10)	

How to represent a random -66 To 66 Random integer between ?

			console.log(Math.ceil(Math.random()*(66-(-66))+(-66)))

Add ：
toFixed Returns a few decimal places after the decimal point , The parameter represents the specific decimal digits
Be careful ： Take the rounded value .

			var n=8.66
			var re=n.toFixed(1)
			var re2=n.toFixed(2)
			console.log(re)
			console.log(re2)

parseFloat Returns a floating-point number in a string
parseInt Returns an integer in a string

			var re2=parseFloat("1239.23px123")
			console.log(re2)
			var re3=parseInt("1239.93px123")
			console.log(re3)

round Rounding off negative numbers （ a key ）

round() Negative numbers, such as ：-11.5 This is in the middle of the decimal .5 Rounding calculation of ：
Math.round(-11.51) = -12
however Math.round(-11.5) = -11; Not at all -12

Math.round() The underlying source code calculation is ：

public static long round(double a) {
    return (long)floor(a + 0.5d);
    }

It can be seen that ,round() The calculation rule is ：
Returns the closest parameter long. The result will be rounded to an integer ： add 0.5, Call... On the result floor And force the result to long type .
therefore :
floor(-11.5+0.5) = -11;
floor(-11.51+0.5) = floo(-12.01) = -12
therefore Math.round(-11.5) = -11, instead of -12