TypeError: not a function at main (__FILE__:20) 求助，这个问题怎么解决。。代码如下

function main() {

for(var i in exchanges){
    var e = exchanges[i];
    var trade = new Trade(i);
    //Log(typeof(P_vol_p), typeof(P_level));
    trade.level = getPara(P_level, i);
    trade.vol_u = P_vol_u;
    trade.contract_value = getPara(P_contract_value, i);
    trade.precision_price = getPara(P_precision_price, i);
    trade.precision_vol = getPara(P_precision_vol, i);
    trade.pos_vol = 0
    trade.pos_price = 0;
    tradeArr.push(trade);
    e.SetContractType("swap");
    e.SetMarginLevel(P_level);
 if(!IsVirtual() ){
        if(!symbolArr)
            var symbolArr = $.get_symbol_arr(e);
        trade.precision_price = symbolArr[e.GetCurrency()].precision_price;
        trade.precision_vol = symbolArr[e.GetCurrency()].precision_vol;
        trade.contract_value = symbolArr[e.GetCurrency()].contract_value;
        trade.min_qty = symbolArr[e.GetCurrency()].min_qty;
        trade.min_val = symbolArr[e.GetCurrency()].min_val;
    
 }
    e.SetPrecision(trade.precision_price, trade.precision_vol)
    Log("设置精度", trade.precision_price, trade.precision_vol);
    e.SetMaxBarLen(500)
}