Javascript function to generate SVG gradient <defs> object

svgGradientDefs.js

/*
  Dependent on d3.js.
*/

const svgGradientDefs = (color_array, gradient_id) => {
  
  if (color_array.length < 2)
    throw new Error("Argument should be array of two or more colors.")

  var pctStep = 100 / (color_array.length - 1),
      stops = color_array.map((d, i) => ({ offset: i * pctStep, color: d }));
  
  const gradient = d3.create("svg"),
        defs = gradient.append("defs");
  
  defs.append("linearGradient")
    .attr("id", gradient_id ? gradient_id : "gradient")
    .selectAll("stop")
    .data(stops)
    .enter()
    .append('stop')
      .attr("offset", d => d.offset + '%')
      .attr("stop-color", d => d.color);
  
  return gradient.node();
  
}