変数を定義し,その後の関数はなぜ変われないのか?

var STATE_IDLE = 0;
var STATE_LONG = 1;
var STATE_SHORT = 2;
var State = STATE_IDLE;

function Trade(currentState, nextState) {

    if (currentState === STATE_IDLE) {
        if (nextState === STATE_LONG) {
            exchange.SetDirection("buy");
            AmountOP = InitAccount.Stocks * 10 / 2;
            exchange.Buy(_C(exchange.GetTicker).Sell, AmountOP);
            State = STATE_LONG;
        }

実行する他の条件も State の値を変えるが,なぜ常に 0 になるのか?