Array.some()

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#1

array .some( function(value, index, arr), this )
Can someone please explain the purpose of index, arr and this?
I think I understand that value returns truthy or falsey, but how do I output the index?
And what does ‘this’ have to do with anything? Here is an example from Codecademy:

const words = [‘unique’, ‘uncanny’, ‘pique’, ‘oxymoron’, ‘guise’];

// Something is missing in the method call below

console.log(words.some((word) => {

return word.length < 6;

}));

In this example, pique is the 1st value that has < 6 letters. That would be index 2. How do I return that to the console? That’s what the index parameter is for right?

#2

The some() method tests whether at least one element in the array passes the test implemented by the provided function. It returns true if, in the array, it finds an element for which the provided function returns true; otherwise it returns false. It doesn’t modify the array.

Which means, you have an array myArray, and you have a function that checks a condition check(). When you call myArray.some(check); you will get a boolean return on whether at least one element of myArray met the condition outlined in check().

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#3

Ive spent almost 2 hours looking at that page, as well as the one on w3. I understand that it checks a condition but what is the index parameter for?

#4

It’s completely optional. This is a very common pattern in js (for the fp functions).
The function iterates on an array, as it iterates, it goes through value-index pairs.

So A = [x,y,z] is going to iterate x: 0, y:1, z:2. arr will always be [x,y,z].

In terms of what it’s good for in this case… it depends.
Toy example: Imagine you have an array A = [“0”, “1”, “10”, “11”, “100”, “x”], and you want to check if there is an element that is not the binary string representation of the index.

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#5

What is the optionality of index. For the love of god what is its purpose? lol

#6

In terms of purpose, think about what a for-loop gives you. You can iterate over a range of numbers and have full access to an array thanks to those. So you have access to: indices, elements of array at those indices, the array itself. Plus you write whatever code you want.

In javascript (and other multi-paradigm languages + functional ones), you have special functions that aim to have a more granular usage. Like filter(), reduce(), some(). These are like for-loops for very specific purposes. You still want to have control over indices, elements, and the array… but when people (or you) read your code and they see you invoke the function they can quickly deduce the reason why you wrote it.

tl;dr: it’s a concise functional style for for-loops.

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#7

In the example above:
console.log(words.some((word) => {

return word.length < 6;

}));

.some(word) the word parameter is the value. if i included .some(word, index) what is the point of that. will it show the index of pique?

#8

It will iterate through the array invoking it, words.

It’s going to look at unique. Index 0. Check condition
pique, index 1, check condition.
etc.

Sometimes it’s useful to have the index depending on what your conditions are.

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#9

I think I have to give up on this for today. Ive spent 2 hours trying to learn 1 simple concept. Thats not very efficient lol. Ty for your help tho.

#10

Well, flip the question, is it useful to have indices while iterating? Ever? If it is, that’s why you have it. What if you wanted to check that every word is larger than the word to the left of it?

words = ['a', 'be', 'cat', 'doge']

You can create a function, is the value at i-1 bigger? But for that you need an index…

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#11

I just wana know how to use it in the example above

#12

If that’s all there is to the example, it’s not used whatsoever.

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#13

will .some() only return true or false. It wont return the index that it was true at?

#14

some() only returns true or false, by definition. It should have no other side effects.

@digital8364790792 what you see in this snippet

(word) => {

return word.length < 6;

}

is the function they are passing to some()

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#15

in the example .some() is true at index 2. how do i print out index 2 to the console

#16

In this case, you run the function without invoking some(). some() just works to validate an assertion.

(that is, iterate over the array and stop when the condition is met, and return the index)

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#17

can you use an example where the index parameter is included?
(word, index) => {
return word.length < 6;
return index //???
}

#18

Pseudocode:

for i = 0 ... array.length in array:
  if condition is met for array[i]:
    return i
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#19

Okay I think this is what I was trying to do:
console.log(words.some((word, index) => {

if(word === ‘pique’){

console.log(index);

}

}));
This prints out
2
false

#20

Even better:
console.log(words.some((word, index) => {

if(word.length < 6){

console.log(index);

}

}));
this prints out
2
4
false

I’m not sure why it prints out false at the end but O well, at least I can move on now.
Thanks for your help