Definition and Usage
定义与用法

The atan() method returns the arctangent of a number as a numeric value between -PI/2 and PI/2 radians.
atan()方法可以返回数字的反正切值

The atan2() method returns the angle theta of an (x,y) point as a numeric value between -PI and PI radians.
atan2()方法可以计算两个变量x 和y 的反正切值

Syntax
语法

Math.atan(x)

Math.atan2(x,y)

Example 1 - atan()
举例

The following example returns the arctangent of different numbers with the atan() method:
不同数值使用atan()方法后返回的值：

<script type="text/javascript">

document.write(Math.atan(0.50) + "<br />")
document.write(Math.atan(-0.50) + "<br />")
document.write(Math.atan(5) + "<br />")
document.write(Math.atan(10) + "<br />")
document.write(Math.atan(-5) + "<br />")
document.write(Math.atan(-10))

</script>

The output of the code above will be:
结果为：

0.4636476090008061
-0.4636476090008061
1.373400766945016
1.4711276743037347
-1.373400766945016
-1.4711276743037347

Example 2 - atan2()
举例 2

The following example returns the angle theta of different (x,y) points with the atan2() method:
使用了atan2()返回不同两变量x,y后的值：

<script type="text/javascript">

document.write(Math.atan2(0.50,0.50) + "<br />")
document.write(Math.atan2(-0.50,-0.50) + "<br />")
document.write(Math.atan2(5,5) + "<br />")
document.write(Math.atan2(10,20) + "<br />")
document.write(Math.atan2(-5,-5) + "<br />")
document.write(Math.atan2(-10,10))

</script>

The output of the code above will be:
上述代码将输出下面的结果：

0.7853981633974483
-2.356194490192345
0.7853981633974483
0.4636476090008061
-2.356194490192345
-0.7853981633974483 

Try-It-Yourself Demos
尝试与演示

atan()
How to use atan() to return the arctangent of different numbers.
如何使用atan()方法

atan2()
How to use atan2() to return the angle theta of different (x,y) points.
如何使用atan2()方法

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