Array.sort() on multiple properties

Question

I have an array, productData with multiple properties. This is how I currently sort the array by monthlyCost, ascending.
How can I modify this to sort all items by a boolean property isPromoted, followed by monthlyCost?
My array should start with all items where isPromoted == true sorted by monthlyCost, then all items where isPromoted == false sorted by monthlyCost.

    productData.sort((a, b) => {
      if (a.monthlyCost > b.monthlyCost) {
        return 1;
      } else if (a.monthlyCost < b.monthlyCost) {
        return -1;
      } else {
        return 0;
      }
    });

if isPromoted is not equal - then return either 1 or -1 - if it is equal, then return the result of your existing comparison — Daniel A. White
– Daniel A. White, Commented Jun 16, 2022 at 14:37
Does this answer your question? How to sort an array of objects by multiple fields? — pilchard
– pilchard, Commented Jun 16, 2022 at 14:51

trincot · Accepted Answer · 2022-06-16 14:41:45Z

3

You can use this callback:

productData.sort((a, b) => +b.isPromoted - +a.isPromoted || a.monthlyCost - b.monthlyCost);

The unary plus is optional in plain JavaScript, but in a TypeScript context, you'll need to be explicit about the conversion to number and apply +.

answered Jun 16, 2022 at 14:41

trincot

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3 Comments

noclist Over a year ago

So why is b minus a for isPromoted but a minus b for monthlyCost?

trincot Over a year ago

Because you want true to come before false, while in numerical order, false (0) would come before (1). So by reversing the expression the order will be as you wish it to be.

noclist Over a year ago

Thank you so much! I'm now trying to throw in another property to sort, promotionLevel which is either 1 or 2. Adding this in to your expression,

productData.sort((a, b) => +b.isPromoted - +a.isPromoted || a.promotionLevel - b.promotionLevel || a.monthlyCost - b.monthlyCost);

doesn't seem to be working as I expect. Can you tell what I'm doing wrong? (I want promotionLevel 1 to come before 2)

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