Refactor traversal to avoid closures

lib/6to5/traverse/index.js

@@ -4,46 +4,34 @@ var Scope = require("./scope");
 var t     = require("../types");
 var _     = require("lodash");
 
-function traverse(parent, opts, scope) {
-  // falsy node
-  if (!parent) return;
+function TraversalContext(previousContext) {
+  this.didSkip = false;
+  this.didRemove = false;
+  this.didStop = false;
+  this.didFlatten = previousContext ? previousContext.didFlatten : false;
+}
 
-  var i, j;
+TraversalContext.prototype.flatten = function () {
+  this.didFlatten = true;
+};
 
-  // array of nodes
-  if (_.isArray(parent)) {
-    for (i = 0; i < parent.length; i++) {
-      traverse(parent[i], opts, scope);
-    }
-    return;
-  }
+TraversalContext.prototype.remove = function () {
+  this.didRemove = true;
+  this.skip();
+};
 
-  // unknown node type to traverse
-  var keys = t.VISITOR_KEYS[parent.type];
-  if (!keys) return;
+TraversalContext.prototype.skip = function () {
+  this.didSkip = true;
+};
 
-  opts = opts || {};
+TraversalContext.prototype.stop = function () {
+  this.didStop = true;
+  this.skip();
+};
 
-  var stopped = false;
-
-  for (i = 0; i < keys.length; i++) {
-    var key = keys[i];
-    var nodes = parent[key];
-    if (!nodes) continue;
-
-    var flatten = false;
-
-    var handle = function (obj, key) {
-      var node = obj[key];
-      if (!node) return;
-
-      // type is blacklisted
-      if (opts.blacklist && opts.blacklist.indexOf(node.type) > -1) return;
-
-      // replace node
-      var maybeReplace = function (result) {
-        if (result === false) return;
-        if (result == null) return;
+TraversalContext.prototype.maybeReplace = function (result, obj, key, node) {
+  if (result === false) return node;
+  if (result == null) return node;
 
   var isArray = _.isArray(result);
 
@@ -55,49 +43,42 @@ function traverse(parent, opts, scope) {
   // replace the node
   node = obj[key] = result;
 
-        if (isArray) flatten = true;
-
   // we're replacing a statement or block node with an array of statements so we better
   // ensure that it's a block
   if (isArray && _.contains(t.STATEMENT_OR_BLOCK_KEYS, key) && !t.isBlockStatement(obj)) {
     t.ensureBlock(obj, key);
   }
-      };
 
-      var skipped = false;
-      var removed = false;
-
-      var context = {
-        stop: function () {
-          skipped = stopped = true;
-        },
-
-        skip: function () {
-          skipped = true;
-        },
-
-        remove: function () {
-          this.skip();
-          removed = true;
+  if (isArray) {
+    this.flatten();
   }
-      };
 
-      //
+  return node;
+};
+
+TraversalContext.prototype.visit = function (obj, key, opts, scope, parent) {
+  var node = obj[key];
+  if (!node) return;
+
+  // type is blacklisted
+  if (opts.blacklist && opts.blacklist.indexOf(node.type) > -1) return;
+
+  var result;
   var ourScope = scope;
   if (t.isScope(node)) ourScope = new Scope(node, scope);
 
   // enter
   if (opts.enter) {
-        var result = opts.enter.call(context, node, parent, ourScope);
-        maybeReplace(result);
+    result = opts.enter.call(this, node, parent, ourScope);
+    node = this.maybeReplace(result, obj, key, node);
 
-        if (removed) {
+    if (this.didRemove) {
       obj[key] = null;
-          flatten = true;
+      this.flatten();
     }
 
-        // stop iteration
-        if (skipped) return;
+    // stop traversal
+    if (this.didSkip) return;
   }
 
   // traverse node
@@ -105,17 +86,42 @@ function traverse(parent, opts, scope) {
 
   // exit
   if (opts.exit) {
-        maybeReplace(opts.exit.call(context, node, parent, ourScope));
+    result = opts.exit.call(this, node, parent, ourScope);
+    node = this.maybeReplace(result, obj, key, node);
   }
-    };
+};
+
+function traverse(parent, opts, scope) {
+  // falsy node
+  if (!parent) return;
+
+  // array of nodes
+  if (_.isArray(parent)) {
+    for (var i = 0; i < parent.length; i++)
+      traverse(parent[i], opts, scope);
+    return;
+  }
+
+  // unknown node type to traverse
+  var keys = t.VISITOR_KEYS[parent.type];
+  if (!keys) return;
+
+  opts = opts || {};
+  var context = null;
+
+  for (var j = 0; j < keys.length; j++) {
+    var key = keys[j];
+    var nodes = parent[key];
+    if (!nodes) continue;
 
     if (_.isArray(nodes)) {
-      for (j = 0; j < nodes.length; j++) {
-        handle(nodes, j);
-        if (stopped) return;
+      for (var k = 0; k < nodes.length; k++) {
+        context = new TraversalContext(context);
+        context.visit(nodes, k, opts, scope, parent);
+        if (context.didStop) return;
       }
 
-      if (flatten) {
+      if (context && context.didFlatten) {
         parent[key] = _.flatten(parent[key]);
 
         if (key === "body") {
@@ -124,8 +130,9 @@ function traverse(parent, opts, scope) {
         }
       }
     } else {
-      handle(parent, key);
-      if (stopped) return;
+      context = new TraversalContext(context);
+      context.visit(parent, key, opts, scope, parent);
+      if (context.didStop) return;
     }
   }
 }