var m = [[1,1,1],[1,1,1],[1,1,1]]
var m2 = [[1,2],[12,1],[5,4],[2,3],[1,2]]
var m3 = [[1,2,3,2],[5,5,1,1],[5,4,2,3],[5,4,2,3],[5,4,2,3]]


function blankBorders(matrix){
    for (let i = 0; i < matrix.length; i++) {
        for (let j = 0; j < matrix[i].length; j++) {
            if(isBorder(i,j,matrix)){
                matrix[i][j] = 0
            }
        }
    }
}

function isBorder(i,j,matrix){
    return i == 0 || i == matrix.length-1 || j == 0 || j == matrix[i].length - 1
}

blankBorders(m)
blankBorders(m2)
blankBorders(m3)
console.log(m);
console.log(m2);
console.log(m3);