JavaScript Math Object

• The Math object allows you to perform mathematical tasks.
• The Math object includes several mathematical methods.

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One common use of the Math object is to create a random number:

Math.random();         // returns a random number 點後.16位 

Math has no constructor. No methods have to create a Math object first.

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Math.min() and Math.max()

Math.min() and Math.max() can be used to find the lowest or highest value in a list of arguments:

Math.min(0, 150, 30, 20, -8);        // returns –8
Math.max(0, 150, 30, 20, -8);       // returns 150

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Math.round()    四捨五入取整數

Math.round() rounds a number to the nearest integer:

Math.round(4.7);            // returns 5
Math.round(4.4);            // returns 4

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Math.ceil()        無條件UP取大整數

Math.ceil() rounds a number up to the nearest integer:

Math.ceil(4.4);             // returns  5
Math.ceil(-4.9);             // returns -4

 

Math.floor()       無條件down取小整數

Math.floor() rounds a number down to the nearest integer:

Math.floor(4.7);            // returns 4
Math.floor(-4.7);            // returns -5

 

Math.floor() and Math.random() can be used together to return a random number between 0 and 10:利用這個方法來得到一個0到10的整數

Math.floor(Math.random() * 11); 
// returns a random number between 0 and 10

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Math Constants 八個常數值

JavaScript provides 8 mathematical constants that can be accessed with the Math object:

Math.E;                     // returns Euler's number
Math.PI                     // returns PI         圓周率
Math.SQRT2             // returns the square root of 2
Math.SQRT1_2          // returns the square root of 1/2
Math.LN2                  // returns the natural logarithm of 2
Math.LN10                // returns the natural logarithm of 10
Math.LOG2E             // returns base 2 logarithm of E
Math.LOG10E           // returns base 10 logarithm of E

Try it Yourself »

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Math Object Methods(真正的數學函數！)

Method	Description
abs(x)	Returns the absolute value of x                                       //絶對值
acos(x)	Returns the arccosine of x, in radians
asin(x)	Returns the arcsine of x, in radians
atan(x)	Returns the arctangent of x as a numeric value between -PI/2 and PI/2 radians
atan2(y,x)	Returns the arctangent of the quotient of its arguments
ceil(x)	Returns x, rounded upwards to the nearest integer
cos(x)	Returns the cosine of x (x is in radians)
exp(x)	Returns the value of Ex
floor(x)	Returns x, rounded downwards to the nearest integer
log(x)	Returns the natural logarithm (base E) of x
max(x,y,z,...,n)	Returns the number with the highest value
min(x,y,z,...,n)	Returns the number with the lowest value
pow(x,y)	Returns the value of x to the power of y                      //次方
random()	Returns a random number between 0 and 1
round(x)	Rounds x to the nearest integer
sin(x)	Returns the sine of x (x is in radians)
sqrt(x)	Returns the square root of x                                          //開根號
tan(x)	Returns the tangent of an angle

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Complete Math Reference

For a complete reference, go to our complete Math object reference.

The reference contains descriptions and examples of all Math properties and methods.