如何在JavaScript中以线性顺序从数组中减去所有项目？

Question

I've been able to get the sum of all items using the following code:

var totalPrice = [60,40];

var total = 0;

   for (var i  = 0; i < totalPrice.length; i++){

      total  += totalPrice[i];

   }

I then tried to subtract all items of the array doing the following:

 totalPrice = [60,40];

var total = 0;

   for (var i  = 0; i < totalPrice.length; i++){

      total  -= totalPrice[i];

   }

This gave me a negative and incorrect output.

How would I subtract all items in an array so that in this example, total would be equal to 20.

Answer 1

It looks like you're not trying to subtract all items from 0, you're trying to subtract all items except the first from the first. This would be a nice place to use reduce :

 const totalPrice = [60, 40]; const total = totalPrice.reduce((a, b) => a - b); console.log(total); 

Using a for loop, you would have to initialize total to the first element, and iterate from the second element onwards:

 const totalPrice = [60, 40]; let total = totalPrice[0]; for (var i = 1; i < totalPrice.length; i++) { total -= totalPrice[i]; } console.log(total); 

Answer 2

Since you mentioned, you don't want to end up with negative result and want to do subtraction in linear order, you should make sure that first item of Array is larger than the sum of all other items in the Array.

And also store the first item of Array in total as below.

 totalPrice = [60,40];

 var total = totalPrice[0];

 for (var i  = 1; i < totalPrice.length; i++){
     total  -= totalPrice[i];
 }

Hope it helps.