Cam someone explain what this statement does? [closed]

  arrays, filter, javascript

I have troubles understanding the meaning of (_,idx) in the following statement

arr.filter((_, idx) => idx % 2 === 0)

I understand it is filtering the array and just returning on the new array all elements that respect the condition(basically with even index). But i do not understand what this (_,idx) means?

Any help?

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