圆的周长与其直径之比,约为3.14159。

PI - 语法

Math.PI 

PI - 示例

console.log(Math.PI)  
//the ratio of a circle's circumference to its diameter: ~3.142           

运行上面代码输出

3.141592653589793            

参考链接

https://www.learnfk.com/es6/es6-math-property-pi.html