function sum(...rest) {    var asum = 0    for (i = 0; i < arguments.length; i++) {        asum += arguments[i]    }    return asum}

function area_of_circle(r, pi) {    var periMeter = 0    // 注意这里用的是==    if ( pi == null){        pi = 3.14    }    periMeter = pi * r * r    return periMeter;}