不确定组合操作员在功能中执行什么操作

Question

我一直在编程以下功能并理解了所有内容，直到这一行。

cost += nightSurcharge; 

我用我if语句条件语句是用来给nightSurcharge添加到晚上8点至早上6点之间的成本。

我需要了解的是+=是否只是说如果满足条件就将nightSurcharge添加到成本？

// 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

我需要了解的是是否+=只是在说加nightSurcharge如果条件满足时的成本？

是，that is exactly correct.此代码是等价的：

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