Question

我在向数组分配值时遇到问题，当我稍后访问该数组插槽时，它返回NaN。

首先，我声明数组如：

    var oldTherms = []; 
    var newTherms = [];
    var oldInputTherms;
    var newInputTherms;

我正在使用变量数据集来计算要分配给oldTherms和newTherms数组的值。我已经验证了计算部分的工作原理并为oldInputTherms和newInputTherms提供了适当的值。我还验证了dataSet.month [i]返回正确的值。但是，下面的switch语句似乎没有向oldTherms []或newTherms []添加累计总计。当我尝试访问newTherms []或oldTherms []时，结果为'NaN'

switch (dataSet.month[i]){
    //subtract 1 in array slot bc months number 1-12 and array slots number 0-11
    case 1: //january
        oldTherms[dataSet.month[i]-1] += oldInputTherms; //add therms to the total used 
        newTherms[dataSet.month[i]-1] += newInputTherms;
        oldKwh[dataSet.month[i]-1] += 0; //no cooling energy calcs
        newKwh[dataSet.month[i]-1] += 0;
        break;
    case 2: //february
        oldTherms[dataSet.month[i]-1] += oldInputTherms; //add therms to the total used
        newTherms[dataSet.month[i]-1] += newInputTherms;
        oldKwh[dataSet.month[i]-1] += 0; //no cooling energy calcs
        newKwh[dataSet.month[i]-1] += 0;
        break;
    case 3: //march
        oldTherms[dataSet.month[i]-1] += oldInputTherms; //add therms to the total used 
        newTherms[dataSet.month[i]-1] += newInputTherms;
        oldKwh[dataSet.month[i]-1] += 0; //no cooling energy calcs
        newKwh[dataSet.month[i]-1] += 0;
        break;
    case 4: //april
        oldTherms[dataSet.month[i]-1] += oldInputTherms; //add therms to the total used 
        newTherms[dataSet.month[i]-1] += newInputTherms;
        oldKwh[dataSet.month[i]-1] += 0; //no cooling energy calcs
        newKwh[dataSet.month[i]-1] += 0;
        break;
    case 5: //may
        oldTherms[dataSet.month[i]-1] += oldInputTherms; //add therms to the total used 
        newTherms[dataSet.month[i]-1] += newInputTherms;
        oldKwh[dataSet.month[i]-1] += 0; //no cooling energy calcs
        newKwh[dataSet.month[i]-1] += 0;
        break;
    case 6: //june
        oldTherms[dataSet.month[i]-1] += oldInputTherms; //add therms to the total used 
        newTherms[dataSet.month[i]-1] += newInputTherms;
        oldKwh[dataSet.month[i]-1] += 0; //no cooling energy calcs
        newKwh[dataSet.month[i]-1] += 0;
        break;
    case 7:  //july
        oldTherms[dataSet.month[i]-1] += oldInputTherms; //add therms to the total used 
        newTherms[dataSet.month[i]-1] += newInputTherms;
        oldKwh[dataSet.month[i]-1] += 0; //no cooling energy calcs
        newKwh[dataSet.month[i]-1] += 0;
        break;
    case 8: //august
        oldTherms[dataSet.month[i]-1] += oldInputTherms; //add therms to the total used 
        newTherms[dataSet.month[i]-1] += newInputTherms;
        oldKwh[dataSet.month[i]-1] += 0; //no cooling energy calcs
        newKwh[dataSet.month[i]-1] += 0;
        break;
    case 9:  //sept
        oldTherms[dataSet.month[i]-1] += oldInputTherms; //add therms to the total used 
        newTherms[dataSet.month[i]-1] += newInputTherms;
        oldKwh[dataSet.month[i]-1] += 0; //no cooling energy calcs
        newKwh[dataSet.month[i]-1] += 0;
        break;
    case 10: //oct
        oldTherms[dataSet.month[i]-1] += oldInputTherms; //add therms to the total used 
        newTherms[dataSet.month[i]-1] += newInputTherms;
        oldKwh[dataSet.month[i]-1] += 0; //no cooling energy calcs
        newKwh[dataSet.month[i]-1] += 0;
        break;
    case 11: //nov
        oldTherms[dataSet.month[i]-1] += oldInputTherms; //add therms to the total used 
        newTherms[dataSet.month[i]-1] += newInputTherms;
        oldKwh[dataSet.month[i]-1] += 0; //no cooling energy calcs
        newKwh[dataSet.month[i]-1] += 0;
        break;
    case 12:  //dec
        oldTherms[dataSet.month[i]-1] += oldInputTherms; //add therms to the total used 
        newTherms[dataSet.month[i]-1] += newInputTherms;
        oldKwh[dataSet.month[i]-1] += 0; //no cooling energy calcs
        newKwh[dataSet.month[i]-1] += 0;
        break;
    default:
        oldTherms[dataSet.month[i]-1] += 0; //add therms to the total used 
        newTherms[dataSet.month[i]-1] += 0;
        oldKwh[dataSet.month[i]-1] += 0; //no cooling energy calcs
        newKwh[dataSet.month[i]-1] += 0;
}

Answer 1

当我尝试访问newTherms []或oldTherms []时，结果是＆＃39; NaN＆＃39;

oldInputTherms，newInputTherms已声明，但未定义，因此这些行

oldTherms[dataSet.month[i]-1] += oldInputTherms;
newTherms[dataSet.month[i]-1] += newInputTherms;

会导致你的NaN。

但是，你说

我已经验证了计算部分的工作原理并为oldInputTherms和newInputTherms提供了适当的值

如果是这样，则可能oldTherms和newTherms未正确初始化。如果是这种情况，请参阅上面的Barmar答案。

Answer 2

您需要初始化数组以包含0：

var oldTherms = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]; 
var newTherms = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0];

否则，您要将newInputTherms和oldInputTherms添加到undefined，其结果为NaN。

返回NaN的数组

2 个答案: