One dimensional array as grid

//one dimensional array as grid
var grid = [];
var numCols = 5;

function get(row, col){
    return grid[row*numCols + col];
}

function set(row, col, value){
    return grid[row*numCols + col] = value;
}

//one dimensional array as grid with stride
//example;  rgba pixel data
function getPixel(x, y){
    var index = (y*imageData.width + x) * 4; //4 integers for RGBA
    var red = imageData[index];
    var green = imageData[index+1];
    var blue = imageData[index+2];
    var alpha = imageData[index+3];
    var alphaPrcnt = alpha/255; //0-1

    var rgba = (red << 24) + (green << 16) + (blue << 8) + (alpha);
    return rgba;
}