diff --git a/lib/compiler/passes/generate-js.js b/lib/compiler/passes/generate-js.js
index 82d1ea4..ed6aff6 100644
--- a/lib/compiler/passes/generate-js.js
+++ b/lib/compiler/passes/generate-js.js
@@ -179,10 +179,8 @@ function generateJS(ast, options) {
           paramsLengthCode = 'bc[ip + ' + (baseLength - 1) + ']';
 
       return [
-        'params = bc.slice(ip + ' + baseLength + ', ip + ' + baseLength + ' + ' + paramsLengthCode + ');',
-        'for (i = 0; i < ' + paramsLengthCode + '; i++) {',
-        '  params[i] = stack[stack.length - 1 - params[i]];',
-        '}',
+        'params = bc.slice(ip + ' + baseLength + ', ip + ' + baseLength + ' + ' + paramsLengthCode + ')',
+        '  .map(function(p) { return stack[stack.length - 1 - p]; });',
         '',
         'stack.splice(',
         '  stack.length - bc[ip + 2],',
@@ -197,13 +195,7 @@ function generateJS(ast, options) {
 
     parts.push([
       'function peg$decode(s) {',
-      '  var bc = new Array(s.length), i;',
-      '',
-      '  for (i = 0; i < s.length; i++) {',
-      '    bc[i] = s.charCodeAt(i) - 32;',
-      '  }',
-      '',
-      '  return bc;',
+      '  return s.split("").map(function(ch) { return ch.charCodeAt(0) - 32; });',
       '}',
       '',
       'function peg$parseRule(index) {'
@@ -218,7 +210,7 @@ function generateJS(ast, options) {
         '      ends     = [],',
         '      stack    = [],',
         '      startPos = peg$currPos,',
-        '      params, i;'
+        '      params;'
       ].join('\n'));
     } else {
       parts.push([
@@ -228,7 +220,7 @@ function generateJS(ast, options) {
         '      end   = bc.length,',
         '      ends  = [],',
         '      stack = [],',
-        '      params, i;'
+        '      params;'
       ].join('\n'));
     }
 
@@ -786,14 +778,11 @@ function generateJS(ast, options) {
       '        },',
       '',
       '        "class": function(expectation) {',
-      '          var escapedParts = "",',
-      '              i;',
-      '',
-      '          for (i = 0; i < expectation.parts.length; i++) {',
-      '            escapedParts += Array.isArray(expectation.parts[i])',
-      '              ? classEscape(expectation.parts[i][0]) + "-" + classEscape(expectation.parts[i][1])',
-      '              : classEscape(expectation.parts[i]);',
-      '          }',
+      '          var escapedParts = expectation.parts.map(function(part) {',
+      '            return Array.isArray(part)',
+      '              ? classEscape(part[0]) + "-" + classEscape(part[1])',
+      '              : classEscape(part);',
+      '          });',
       '',
       '          return "[" + (expectation.inverted ? "^" : "") + escapedParts + "]";',
       '        },',
@@ -846,13 +835,9 @@ function generateJS(ast, options) {
       '  }',
       '',
       '  function describeExpected(expected) {',
-      '    var descriptions = new Array(expected.length),',
+      '    var descriptions = expected.map(describeExpectation),',
       '        i, j;',
       '',
-      '    for (i = 0; i < expected.length; i++) {',
-      '      descriptions[i] = describeExpectation(expected[i]);',
-      '    }',
-      '',
       '    descriptions.sort();',
       '',
       '    if (descriptions.length > 0) {',
diff --git a/lib/parser.js b/lib/parser.js
index 873f854..3dfcadd 100644
--- a/lib/parser.js
+++ b/lib/parser.js
@@ -36,14 +36,11 @@ peg$SyntaxError.buildMessage = function(expected, found) {
         },
 
         "class": function(expectation) {
-          var escapedParts = "",
-              i;
-
-          for (i = 0; i < expectation.parts.length; i++) {
-            escapedParts += Array.isArray(expectation.parts[i])
-              ? classEscape(expectation.parts[i][0]) + "-" + classEscape(expectation.parts[i][1])
-              : classEscape(expectation.parts[i]);
-          }
+          var escapedParts = expectation.parts.map(function(part) {
+            return Array.isArray(part)
+              ? classEscape(part[0]) + "-" + classEscape(part[1])
+              : classEscape(part);
+          });
 
           return "[" + (expectation.inverted ? "^" : "") + escapedParts + "]";
         },
@@ -96,13 +93,9 @@ peg$SyntaxError.buildMessage = function(expected, found) {
   }
 
   function describeExpected(expected) {
-    var descriptions = new Array(expected.length),
+    var descriptions = expected.map(describeExpectation),
         i, j;
 
-    for (i = 0; i < expected.length; i++) {
-      descriptions[i] = describeExpectation(expected[i]);
-    }
-
     descriptions.sort();
 
     if (descriptions.length > 0) {