javascript - 不确定组合运算符在函数中的作用

Question

我一直在编写以下函数，并且理解了这一行之前的所有内容。

   cost += nightSurcharge;

我在我的if语句中使用了条件句，用于在晚上 8 点到早上 6 点之间将 nightSurcharge 添加到成本中。

我需要了解的是+=，如果满足条件，是否只是说将 nightSurcharge 添加到成本中？

// add a parameter called hourOfDay to the function
    var taxiFare = function (milesTraveled, hourOfDay) {
      var baseFare = 2.50;
      var costPerMile = 2.00;
      var nightSurcharge = 0.50; // 8pm to 6am, every night

      var cost = baseFare + (costPerMile * milesTraveled);

      // add the nightSurcharge to the cost starting at 
      // 8pm (20) or if it is before 6am (6)
       if (hourOfDay >= 20 || hourOfDay < 6) {
          cost += nightSurcharge;
      } 

      return cost;

    };

Answer 1

我需要了解的是+=，如果满足条件，是否只是说将 nightSurcharge 添加到成本中？

是的，这完全正确。这段代码是等价的：

if (hourOfDay >= 20) {
    cost = cost + nightSurcharge;
}
else if (hourOfDay < 6) {
    cost = cost + nightSurcharge;
}