My solution to https://www.hackerrank.com/challenges/cavity-map/problem

cavityMap.js

function cavityMap(grid) {
    // Turn grid into a 2D array
    const twoDArr = grid.map(ele => ele.split(''));
    
    // Loop through 2D array checking values against neighbours
    for(let i = 1; i < twoDArr.length - 1; i++) {
        for(let j = 1; j < twoDArr[i].length - 1; j++) {
            if(horizontalCheck(twoDArr, i, j) && verticalCheck(twoDArr, i, j)) {
              twoDArr[i][j] = 'X'; 
            }
        }
    }
    const newGrid = twoDArr.map(ele => ele.join(''));
    return newGrid;
}

// Check against horizontal values
function horizontalCheck(arr, column, row) {
    if(arr[column][row] > arr[column][row - 1] && arr[column][row] > arr[column][row + 1]) {
        return true;
    } else {
        return false;
    }
}

// Check against vertical values
function verticalCheck(arr, column, row) {
    if(arr[column][row] > arr[column - 1][row] && arr[column][row] > arr[column + 1][row]) {
        return true;
    } else {
        return false;
    }
}