For loop does not iterate over sub-arrays

JavaScript
#1

Tell us what’s happening:
the second for loop does not iterate over the arr indexes just like the first for loop does

Your code so far


function largestOfFour(arrs) {
let max = 0;
for (const arr in arrs) {
    console.log(`arrs[${arr}]: ${arrs[arr]}`)
    for (const numb in arr) {
        // console.log("arr[numb]: " + arrs[arr][numb])
        console.log(`arrs[${arr}][${numb}]: ${arrs[arr][numb]}`)
        //   if(max<arrs[arr[numb]])
    }
}
return arrs;
}

largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);

** Output **

arrs[0]: 4,5,1,3
arrs[0][0]: 4
arrs[1]: 13,27,18,26
arrs[1][0]: 13
arrs[2]: 32,35,37,39
arrs[2][0]: 32
arrs[3]: 1000,1001,857,1
arrs[3][0]: 1000

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Challenge: Return Largest Numbers in Arrays

Link to the challenge:

#2

it turns out that it must be for(const numb in arrs[arr])