helpme.please.js

String.prototype.replaceAt = function(index, character) {
    return this.substr(0, index) + character + this.substr(index + character.length);
}

var instructions = document.body.textContent.split('\n');
var grid = [];
//create grid
for (var a = 0; a < 6; a++) {
    grid.push(Array(51).join("0"));
}

instructions.forEach(function(item) {
    if (item.split(' ')[0] == "rotate") {
        if (item.split(" ")[1] == "row") {
            var row = Number(item.charAt(item.indexOf("=") + 1));
            var dis = Number(item.split(" ")[item.split(" ").length - 1]);
            shiftRowRight(row, dis);
        } else {
            var row = Number(item.charAt(item.indexOf("=") + 1));
            var dis = Number(item.split(" ")[item.split(" ").length - 1]);
            shiftRowDown(row, dis);
        }
    } else {
        if (item) {
            var p1 = Number(item.split(' ')[1].split('x')[0]);
            var p2 = Number(item.split(' ')[1].split('x')[1]);
            makeRect(p1, p2);
        }
    }
});

function makeRect(w, h) {
    for (var b = 0; b < h; b++) {
        for (var c = 0; c < w; c++) {
            grid[b] = grid[b].replaceAt(c, "1");
        }
    }
}

function shiftRowRight(row, dis) {
    var ar = grid[row].split('');
    ar = ar.concat(ar.splice(0, ar.length - dis));
    grid[row] = ar.join("");
}

function shiftRowDown(col, dis) {
    var arr = [];
    grid.forEach(function(row) {
        arr.push(row.charAt(col));
    });
    arr = arr.concat(arr.splice(0, arr.length - dis));
    for (var d = 0; d < grid.length; d++) {
        grid[d] = grid[d].replaceAt(col, arr[d]);
    }
}

//find answer
var answer = 0;
grid.forEach(function(finalRow) {
    answer += (finalRow.match(/1/g) || []).length;
});
console.log(grid.toString());