Grid with single index

Hello, what's the best way to make a grid by Javascript and HTML? I need to be able to draw or change the area color of each blank space. I made it that way but it does not answer because when I try to change the color of a single square it ends up changing either the entire line or the entire column.

for(var i = 0;i < linha;i++) {
    for (var n = 0;n < coluna;n++) {
        grid_x[i] = i * 40;
        grid_y[n] = n * 40;
        res_x[i] = i * 40;
        res_y[n] = n * 40;
        c[i] = false * i
        dRs(grid_x[i],grid_y[n],grid_w,grid_h,1,"#747474",c[i])
    }
}
function dRs(x,y,w,h,l,s,c) {
    context.beginPath();
    context.lineWidth= l;
    context.strokeStyle= s;
    context.rect(x,y,w,h);      
    context.stroke();
}