Double quotes used for strings in the last whitespace example var leds = stage.selectAll('.led') .data(data) .enter().append("svg:svg") .class('led', true) .attr('width', (radius + margin) \* 2) .append("svg:g") .attr("transform", "translate(" + (radius + margin) + "," + (radius + margin) + ")") .call(tron.led);