diff --git a/lib/svgo.js b/lib/svgo.js
index 24a88678..ca364191 100755
--- a/lib/svgo.js
+++ b/lib/svgo.js
@@ -10,48 +10,52 @@
  * @license MIT https://raw.githubusercontent.com/svg/svgo/master/LICENSE
  */
 
-var CONFIG = require('./svgo/config.js'),
-    SVG2JS = require('./svgo/svg2js.js'),
-    PLUGINS = require('./svgo/plugins.js'),
-    JSAPI = require('./svgo/jsAPI.js'),
-    encodeSVGDatauri = require('./svgo/tools.js').encodeSVGDatauri,
-    JS2SVG = require('./svgo/js2svg.js');
+const { resolvePluginConfig } = require('./svgo/config.js');
+const SVG2JS = require('./svgo/svg2js.js');
+const PLUGINS = require('./svgo/plugins.js');
+const JSAPI = require('./svgo/jsAPI.js');
+const { encodeSVGDatauri } = require('./svgo/tools.js');
+const JS2SVG = require('./svgo/js2svg.js');
 
-var SVGO = function(config) {
-    this.config = CONFIG(config);
+var SVGO = function(config = {}) {
+  this.config = config;
 };
 
 SVGO.prototype.optimize = function(svgstr, info = {}) {
-    const config = this.config;
-    if (config.error) {
-        throw Error(config.error);
+  const config = this.config;
+  if (typeof config !== 'object') {
+    throw Error('Config should be an object')
+  }
+  const maxPassCount = config.multipass ? 10 : 1;
+  let prevResultSize = Number.POSITIVE_INFINITY;
+  let svgjs = null;
+  for (let i = 0; i < maxPassCount; i += 1) {
+    svgjs = SVG2JS(svgstr);
+    if (svgjs.error == null && config.plugins) {
+      if (Array.isArray(config.plugins) === false) {
+        throw Error('Invalid plugins list. Provided \'plugins\' in config should be an array.');
+      }
+      const plugins = config.plugins.map(plugin => resolvePluginConfig(plugin, config))
+      svgjs = PLUGINS(svgjs, info, plugins);
     }
-    const maxPassCount = config.multipass ? 10 : 1;
-    let prevResultSize = Number.POSITIVE_INFINITY;
-    let svgjs = null;
-    for (let i = 0; i < maxPassCount; i += 1) {
-        svgjs = SVG2JS(svgstr);
-        if (svgjs.error == null) {
-            svgjs = PLUGINS(svgjs, info, config.plugins);
-        }
-        svgjs = JS2SVG(svgjs, config.js2svg);
-        if (svgjs.error) {
-            throw Error(svgjs.error);
-        }
-        info.multipassCount = i;
-        if (svgjs.data.length < prevResultSize) {
-            prevResultSize = svgjs.data.length
-        } else {
-            if (config.datauri) {
-                svgjs.data = encodeSVGDatauri(svgjs.data, config.datauri);
-            }
-            if (info && info.path) {
-                svgjs.path = info.path;
-            }
-            return svgjs;
-        }
+    svgjs = JS2SVG(svgjs, config.js2svg);
+    if (svgjs.error) {
+      throw Error(svgjs.error);
     }
-    return svgjs;
+    info.multipassCount = i;
+    if (svgjs.data.length < prevResultSize) {
+      prevResultSize = svgjs.data.length
+    } else {
+      if (config.datauri) {
+        svgjs.data = encodeSVGDatauri(svgjs.data, config.datauri);
+      }
+      if (info && info.path) {
+        svgjs.path = info.path;
+      }
+      return svgjs;
+    }
+  }
+  return svgjs;
 };
 
 /**
@@ -64,8 +68,6 @@ SVGO.prototype.createContentItem = function(data) {
     return new JSAPI(data);
 };
 
-SVGO.Config = CONFIG;
-
 module.exports = SVGO;
 // Offer ES module interop compatibility.
 module.exports.default = SVGO;
diff --git a/lib/svgo/config.js b/lib/svgo/config.js
index 2876f617..d0d5b3ff 100644
--- a/lib/svgo/config.js
+++ b/lib/svgo/config.js
@@ -2,52 +2,11 @@
 
 const pluginsMap = require('../../plugins/plugins.js');
 
-/**
- * Read and/or extend/replace default config file,
- * prepare and optimize plugins array.
- *
- * @param {Object} [config] input config
- * @return {Object} output config
- */
-module.exports = function(config) {
-
-    var defaults;
-    config = typeof config == 'object' && config || {};
-
-    if (config.plugins && !Array.isArray(config.plugins)) {
-        return { error: 'Error: Invalid plugins list. Provided \'plugins\' in config should be an array.' };
-    }
-
-    defaults = config;
-
-    if (Array.isArray(defaults.plugins)) {
-        defaults.plugins = defaults.plugins.map(resolvePluginConfig);
-    }
-
-    if ('floatPrecision' in config && Array.isArray(defaults.plugins)) {
-        defaults.plugins.forEach(function(plugin) {
-            if (plugin.params && ('floatPrecision' in plugin.params)) {
-                // Don't touch default plugin params
-                plugin.params = Object.assign({}, plugin.params, { floatPrecision: config.floatPrecision });
-            }
-        });
-    }
-
-    if ('datauri' in config) {
-        defaults.datauri = config.datauri;
-    }
-
-    if (Array.isArray(defaults.plugins)) {
-        defaults.plugins = optimizePluginsArray(defaults.plugins);
-    } else {
-      defaults.plugins = [];
-    }
-
-    return defaults;
-
-};
-
-const resolvePluginConfig = plugin => {
+const resolvePluginConfig = (plugin, config) => {
+  let configParams = {};
+  if ('floatPrecision' in config) {
+    configParams.floatPrecision = config.floatPrecision;
+  }
   if (typeof plugin === 'string') {
     // resolve builtin plugin specified as string
     const pluginConfig = pluginsMap[plugin];
@@ -58,7 +17,7 @@ const resolvePluginConfig = plugin => {
       ...pluginConfig,
       name: plugin,
       active: true,
-      params: { ...pluginConfig.params }
+      params: { ...pluginConfig.params, ...configParams }
     };
   }
   if (typeof plugin === 'object' && plugin != null) {
@@ -70,7 +29,7 @@ const resolvePluginConfig = plugin => {
       return {
         active: true,
         ...plugin,
-        params: { ...plugin.params }
+        params: { configParams, ...plugin.params }
       };
     } else {
       // resolve builtin plugin specified as object without implementation
@@ -82,30 +41,10 @@ const resolvePluginConfig = plugin => {
         ...pluginConfig,
         active: true,
         ...plugin,
-        params: { ...pluginConfig.params, ...plugin.params }
+        params: { ...pluginConfig.params, ...configParams, ...plugin.params }
       };
     }
   }
   return null;
 };
-
-/**
- * Try to group sequential elements of plugins array.
- *
- * @param {Object} plugins input plugins
- * @return {Array} output plugins
- */
-function optimizePluginsArray(plugins) {
-
-    var prev;
-
-    return plugins.reduce(function(plugins, item) {
-        if (prev && item.type == prev[0].type) {
-            prev.push(item);
-        } else {
-            plugins.push(prev = [item]);
-        }
-        return plugins;
-    }, []);
-
-}
+exports.resolvePluginConfig = resolvePluginConfig;
diff --git a/lib/svgo/plugins.js b/lib/svgo/plugins.js
index a317f5b6..21a85028 100644
--- a/lib/svgo/plugins.js
+++ b/lib/svgo/plugins.js
@@ -11,25 +11,33 @@
  * @return {Object} output data
  */
 module.exports = function(data, info, plugins) {
-
-    plugins.forEach(function(group) {
-
-        switch(group[0].type) {
-            case 'perItem':
-                data = perItem(data, info, group);
-                break;
-            case 'perItemReverse':
-                data = perItem(data, info, group, true);
-                break;
-            case 'full':
-                data = full(data, info, group);
-                break;
-        }
-
-    });
-
-    return data;
-
+  const perItemPlugins = [];
+  const perItemReversePlugins = [];
+  const fullPlugins = [];
+  // Try to group sequential elements of plugins array
+  for (const plugin of plugins) {
+    switch(plugin.type) {
+      case 'perItem':
+        perItemPlugins.push(plugin);
+        break;
+      case 'perItemReverse':
+        perItemReversePlugins.push(plugin);
+        break;
+      case 'full':
+        fullPlugins.push(plugin);
+        break;
+    }
+  }
+  if (perItemPlugins.length !== 0) {
+    data = perItem(data, info, perItemPlugins);
+  }
+  if (perItemReversePlugins.length !== 0) {
+    data = perItem(data, info, perItemReversePlugins, true);
+  }
+  if (fullPlugins.length !== 0) {
+    data = full(data, info, fullPlugins);
+  }
+  return data;
 };
 
 /**
diff --git a/plugins/plugins.js b/plugins/plugins.js
index 20c03508..a64a0384 100644
--- a/plugins/plugins.js
+++ b/plugins/plugins.js
@@ -1,3 +1,5 @@
+'use strict';
+
 exports.addAttributesToSVGElement = require('./addAttributesToSVGElement.js');
 exports.addClassesToSVGElement = require('./addClassesToSVGElement.js');
 exports.cleanupAttrs = require('./cleanupAttrs.js');
diff --git a/test/config/_index.js b/test/config/_index.js
index b76c206c..136b3bd6 100644
--- a/test/config/_index.js
+++ b/test/config/_index.js
@@ -1,46 +1,20 @@
 'use strict';
 
 const { expect } = require('chai');
-
-var CONFIG = require('../../lib/svgo/config');
+const { resolvePluginConfig } = require('../../lib/svgo/config.js');
 
 describe('config', function() {
 
-    describe('default config', function() {
-
-        var config = CONFIG();
-
-        it('should be an instance of Object', function() {
-            expect(config).to.be.an.instanceOf(Object);
-        });
-
-        it('should have property "plugins"', function() {
-            expect(config).to.have.property('plugins');
-        });
-
-        it('"plugins" should be an instance of Array', function() {
-            expect(config.plugins).to.be.an.instanceOf(Array);
-        });
-
-    });
-
     describe('extend config with object', function() {
 
-        var config = CONFIG({
-                multipass: true,
-                plugins: [
-                    { name: 'removeDoctype', active: false },
-                    { name: 'convertColors', params: { shorthex: false } },
-                    { name: 'removeRasterImages', params: { param: true } }
-                ]
-            }),
-            removeDoctype = getPlugin('removeDoctype', config.plugins),
-            convertColors = getPlugin('convertColors', config.plugins),
-            removeRasterImages = getPlugin('removeRasterImages', config.plugins);
-
-        it('should have "multipass"', function() {
-            expect(config.multipass).to.be.true;
-        });
+        var plugins = [
+            { name: 'removeDoctype', active: false },
+            { name: 'convertColors', params: { shorthex: false } },
+            { name: 'removeRasterImages', params: { param: true } }
+        ].map(plugin => resolvePluginConfig(plugin, {}));
+        const removeDoctype = getPlugin('removeDoctype', plugins);
+        const convertColors = getPlugin('convertColors', plugins);
+        const removeRasterImages = getPlugin('removeRasterImages', plugins);
 
         it('removeDoctype plugin should be disabled', function() {
             expect(removeDoctype.active).to.be.false;
@@ -90,21 +64,22 @@ describe('config', function() {
 
     describe('replace default config with custom', function() {
 
-        var config = CONFIG({
-                multipass: true,
-                floatPrecision: 2,
-                plugins: [
-                    { name: 'cleanupNumericValues' }
-                ]
-            }),
-            cleanupNumericValues = getPlugin('cleanupNumericValues', config.plugins);
+        const config = {
+            multipass: true,
+            floatPrecision: 2,
+            plugins: [
+                { name: 'cleanupNumericValues' }
+            ]
+        }
+        const plugins = config.plugins.map(plugin => resolvePluginConfig(plugin, config));
+        const cleanupNumericValues = getPlugin('cleanupNumericValues', plugins);
 
         it('should have "multipass"', function() {
             expect(config.multipass).to.be.true;
         });
 
         it('config.plugins should have length 1', function() {
-            expect(config.plugins).to.have.length(1);
+            expect(plugins).to.have.length(1);
         });
 
         it('cleanupNumericValues plugin should be enabled', function() {
@@ -121,16 +96,14 @@ describe('config', function() {
     describe('custom plugins', function() {
 
         describe('extend config with custom plugin', function() {
-            var config = CONFIG({
-                    plugins: [
-                        {
-                            name: 'aCustomPlugin',
-                            type: 'perItem',
-                            fn: function() { }
-                        }
-                    ]
-                }),
-                customPlugin = getPlugin('aCustomPlugin', config.plugins);
+            const plugins = [
+                {
+                    name: 'aCustomPlugin',
+                    type: 'perItem',
+                    fn: function() { }
+                }
+            ].map(plugin => resolvePluginConfig(plugin, {}));
+            const customPlugin = getPlugin('aCustomPlugin', plugins);
 
             it('custom plugin should be enabled', function() {
                 expect(customPlugin.active).to.be.true;
@@ -143,19 +116,17 @@ describe('config', function() {
 
         describe('replace default config with custom plugin', function() {
 
-            var config = CONFIG({
-                    plugins: [
-                        {
-                            name: 'aCustomPlugin',
-                            type: 'perItem',
-                            fn: function() { }
-                        }
-                    ]
-                }),
-                customPlugin = getPlugin('aCustomPlugin', config.plugins);
+            const plugins = [
+                {
+                    name: 'aCustomPlugin',
+                    type: 'perItem',
+                    fn: function() { }
+                }
+            ].map(plugin => resolvePluginConfig(plugin, {}));
+            const customPlugin = getPlugin('aCustomPlugin', plugins);
 
             it('config.plugins should have length 1', function() {
-                expect(config.plugins).to.have.length(1);
+                expect(plugins).to.have.length(1);
             });
 
             it('custom plugin should be enabled', function() {
@@ -173,18 +144,10 @@ describe('config', function() {
 });
 
 function getPlugin(name, plugins) {
-
-    var found;
-
-    plugins.some(function(group) {
-        return group.some(function(plugin) {
-            if (plugin.name === name) {
-                found = plugin;
-                return true;
-            }
-        });
+    return plugins.find(function(plugin) {
+        if (plugin.name === name) {
+            return plugin;
+        }
     });
 
-    return found;
-
 }