'use strict';

function area_of_circle(r, pi) {
    var area = 0
    if (arguments.length === 1) {
        area = Math.pow(r, 2) * 3.14
    }
    else area = Math.pow(r, 2) * pi

    return area;
}
// 测试:
if (area_of_circle(2) === 12.56 && area_of_circle(2, 3.1416) === 12.5664) {
    alert('测试通过');
} else {
    alert('测试失败');
}