index.js

var through2 = require('through2');
var _ = require('lodash');
var fs = require( 'fs' );

module.exports = function (opts) {
  return through2.obj(function (chunk, enc, callback) {
    var string = chunk.toString(),
      regex = /<img(?:.*?)>/g,
      foundImgs = string.match(regex);

    if ( foundImgs ) {
      var foundSvgs =_.filter(foundImgs, function( it ) {
        return _.includes(it, 'data-inline-svg');
      });

      if ( foundSvgs && foundSvgs.length > 0 ) {
        _.each(foundSvgs, function( it ) {
          var srcMatch = /src=(?:"|\\'|')/;
          var classMatch = /class=(?:"|\\'|')/;
          var endMatch = /(?:"|\\'|')/;

          var filePath = opts.basePath + it.split( srcMatch )[1].split( endMatch )[0];
          var contents = fs.readFileSync(filePath, 'utf8');

          if ( _.includes(it, 'class="') ) {
            var classes = it.split( classMatch )[1].split( endMatch )[0];
            var classString = 'class="' + classes + '" ';

            contents = contents.replace('<svg', '<svg ' + classString);
          }

          string = string.replace( it, contents.trim() );
        });
      }
    }

    this.push(string);

    callback();
  });
};