I don't know this syntax and cant find it. Please just give me a hint where to read about it

the syntax.

const findMyKeys = arr => arr.findIndex(item => item === ‘keys’)

Actually I can’t figoure out the two arrows. I belive its stg easy but still I’m missing something. But for days I can’t go on with the exercises because of this …

MDN has good documentation on JS, including the arrow function:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions

but then the 2 arrows are only just a function in a function?

yes, except in your code you have a method call (findIndex) inside the body of your findMyKeys

this method takes a (callback) function as argument.

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