How to draw lines thicker than 1px

This is a JS snippet how to draw lines with lineWidthh using this function:

function fillLine(x1, y1, x2, y2, lineWidth) {

    var dx, dy, d;

    if (!lineWidth) {
        g.drawLine(x1, y1, x2, y2);
    } else {
        lineWidth = (lineWidth - 1) / 2;
        dx = x2 - x1;
        dy = y2 - y1;
        d = Math.sqrt(dx * dx + dy * dy);
        dx = Math.round(dx * lineWidth / d, 0);
        dy = Math.round(dy * lineWidth / d, 0);

        g.fillPoly([x1 + dx, y1 - dy, x1 - dx, y1 + dy, x2 - dx, y2 + dy, x2 + dx, y2 - dy], true);
    }
}
g.clear();

fillLine(20, 20, 150, 150, 10);

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