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Already had a certain exercise when we mapped our users in the one of previous videos, but here I want

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to talk about certain a little bit different.

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As you can see, you can get the questions answered.

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The array of numbers,

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which actually means we have an array, for example, three, five, one and one was sorted.

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And for this, we're using certain function in JavaScript.

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So we're simpler, I saw.

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And here we must pass a searchable function and we have such conditions when a less than they were written

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here minus one.

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If a greater than B than one and zero, if they're equal and previously brought here A and B and here

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we can write a smaller than B, then we're returning minus one in that the keys were written in one.

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Also, it is important to remember that certain returns the result of the certain, which means we can

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put it in a variable, for example, a result, but it will also mutate our array that we created.

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And actually, it doesn't really make sense here because this has generated a on the fly.

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But if people put it in the variable, then it makes sense.

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Here we have our array and here we are searching it.

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Let's look in the example I'm going to log in here array and result.

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And as you can see in browser here, we are getting exactly the same sorted the rate and this is happening

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because sort of mutates existing array and we must remember about it.

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Also, there is one more important point to remember in compare function, we can return a number which

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is bigger than zero and smaller than zero, and it will be exactly the same.

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It will sort of be before a sort, a before B, which actually means we can write our code a little

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bit differently and not with minus one and one.

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We can simply return here a minus B.

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Why is that?

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Because we have here two numbers, for example, three minus five.

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In this case, it will be less than zero and then we will have this condition sort a before B.

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Let's check this out.

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Time to load in the page.

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We're getting one three five as previously, if people right here b minus A.

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Then it will be sorted in the direction, as you can see where getting five through one, which actually

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means for certain we can sorted by returning minus one and one or something less than zero and bigger

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than zero.

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Also, it is important to remember that we can use certain on Lewis primitives if you are trying to

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sort here and object, it won't do anything because you can't really compare objects, but you can sort

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properties, incite objects, and we have a task to sort an array of our books by authors last name.

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And here we can use exactly the same search and function.

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So we're right in here.

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Books, dot sort.

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And here we're getting as an argument, book one and book two.

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And now we must compare them properly.

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So first of all, we must find a last name of the first author and of the second author.

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So he'll it's right.

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Also, last name one.

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And here we are taking our book one dot author.

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And here we want to split our name with space and get here.

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First argument.

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In this case, we will get to the last name of our author.

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Now I will copy paste this line, and here we have author last name too.

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And here is the book too.

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And now after this, we can compare this to strains.

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This is why here we can write our last name one smaller than our thought last name all.

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Then we want to return minus one.

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In the other case, we will return one.

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And actually, as you can see here, we must use minus one and one because it's not numbers.

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We can't really subtract strains.

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And as you can see here in Tulsa, we didn't console.log anything.

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Now let's console.log our books because actually, we mutated our rate.

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Let's reload the page.

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And as you can see, these are our books, but not on the first place.

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We have Susan Collins.

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As you can see, it is sorted because previously we had control and then measured.

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And then John Jolin, which actually means this code is working and this is how you certain array of

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objects by some property.