analyze-css/rules/base64.js

CSS selectors complexity and performance analyzer

"use strict";

var format = require("util").format,
  MAX_LENGTH = 4 * 1024;

/**
 * @param { import("../lib/css-analyzer") } analyzer
 */
function rule(analyzer) {
  var re = /data:[^/]+\/([^;]+)(?:;charset=[^;]+)?;base64,([^)]+)/;
  analyzer.setMetric("base64Length");

  analyzer.on("declaration", function (rule, property, value) {
    var base64, buf, matches;

    if (re.test(value)) {
      // parse data URI
      matches = value.match(re);
      base64 = matches[2];
      buf = Buffer.from(base64, "base64");

      analyzer.incrMetric("base64Length", base64.length);

      if (base64.length > MAX_LENGTH) {
        analyzer.addOffender(
          "base64Length",
          format(
            "%s { %s: ... } // base64: %s kB, raw: %s kB",
            rule.selectors.join(", "),
            property,
            (base64.length / 1024).toFixed(2),
            (buf.length / 1024).toFixed(2),
          ),
        );
      }
    }
  });
}

rule.description = "Reports on base64-encoded images";
module.exports = rule;