求圆的面积

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#1 Created at ... [Delete] [Delete and Lock User]

function area_of_circle(r, pi) { return rr( arguments.length >= 2 ? pi : 3.14 ); }

#2 Created at ... [Delete] [Delete and Lock User]

告诉你一个更简洁的方法：

return r * r * (pi || 3.14);

#3 Created at ... [Delete] [Delete and Lock User]

function create_counter(initial) { var x = initial || 0; return { inc: function () { x += 1; return x; } } }

包括你说的这个

return r r (pi || 3.14);

感觉不太好理解

x || 0 或者 x || 3.14

返回的结果不应该是个布尔值，真值吗？

#4 Created at ... [Delete] [Delete and Lock User]

在有一个操作数不是布尔值的情况下，不一定返回布尔值，会遵循一些规则。

#5 Created at ... [Delete] [Delete and Lock User]

“false, 0, undefined, null, ''”都会返回false,不传值就是undefined返回false,得到“||”后面的值

||前面为true,不管||后面是true还是false，都返回||前面的值 ||前面为false,不管||后面是true还是false，都返回||后面的值