Exams - Reveal Triangles

/* You are given a sequence of text lines, holding small Latin letters. Your task is to reveal all triangles
in the text by changing their letters with '*'. Triangles consist of equal letters in the form of triangle.
 Triangles can span different sizes: 2 lines, 3 lines, 4 lines, etc. Triangles can overlap (some letters
 can take part in several triangles). Print at the console the input data after replacing all triangles by '*'. */

"use strict";

function revealTriangles(arr) {
    for (var i = 0; i < arr.length; i += 1) {
        arr[i] = arr[i].split('').filter(Boolean);
    }

    function clone(obj) {
        var deepCopyObj = new obj.constructor();
        for (var property in obj) {
            if (obj.hasOwnProperty(property)) {
                switch (typeof obj[property]) {
                    case 'object':
                        deepCopyObj[property] = clone(obj[property]);
                        break;
                    default:
                        deepCopyObj[property] = obj[property];
                        break;
                }
            }
        }

        return deepCopyObj;
    }
    var output = clone(arr);

    for (var row = 0; row < arr.length; row += 1) {
        for (var col = 0; col < arr[row].length; col += 1) {
            if (row + 1 < arr.length && col - 1 >= 0 && col + 1 < arr[row + 1].length &&
                arr[row][col] == arr[row + 1][col - 1] && arr[row][col] == arr[row + 1][col] &&
                arr[row][col] == arr[row + 1][col + 1]) {
                output[row][col] = '*';
                output[row + 1][col - 1] = '*';
                output[row + 1][col] = '*';
                output[row + 1][col + 1] = '*';
            }
        }
        output[row] = output[row].join('');
    }
    return output.join('\n');
}

console.log(revealTriangles([
    'abcdexgh',
    'bbbdxxxh',
    'abcxxxxx'
]));

console.log(revealTriangles([
    'aa',
    'aaa',
    'aaaa',
    'aaaaa'
]));

console.log(revealTriangles([
    'ax',
    'xxx',
    'b',
    'bbb',
    'bbbb'
]));