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Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs. This binary checks for style issues such as incorrect or missing JSDoc usage, and missing goog.require() statements. It does not do more advanced checks such as typechecking.

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/*
 * Copyright 2008 The Closure Compiler Authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.javascript.jscomp;

import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.ListMultimap;
import com.google.common.collect.Lists;
import com.google.common.collect.Multimaps;
import com.google.javascript.jscomp.NodeTraversal.Callback;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import java.util.List;
import java.util.Map.Entry;

/**
 * Moves top-level function declarations to the top of the enclosing JSModule.
 *
 * Enable this pass if a try catch block wraps the output after compilation, and the output runs
 * on Firefox because function declarations are only defined when reached inside a try catch block
 * on older versions of Firefox.
 *
 * 
On Firefox versions <= 45, this code works:
 *
 * 
var g = f; function f() {}
 *
 * 
but this code does not work:
 *
 * 
try { var g = f; function f() {} } catch(e) {}
 *
 * 
NOTE(lharker): As of Firefox version 46 the above code works. Projects not supporting older
 * versions of Firefox shouldn't need this pass.
 *
 * 
RescopeGlobalSymbols still depends on this pass running first to preserve function hoisting
 * semantics.
 *
 * NOTE(dimvar): This pass is safe to turn on by default and delete the associated compiler
 * option. However, we don't do that because the pass is only useful for code wrapped in a
 * try/catch, and otherwise it makes debugging harder because it moves code around.
 *
 */
class MoveFunctionDeclarations implements Callback, CompilerPass {
  private final AbstractCompiler compiler;
  private final ListMultimap functions;

  MoveFunctionDeclarations(AbstractCompiler compiler) {
    this.compiler = compiler;
    functions = ArrayListMultimap.create();
  }

  @Override
  public void process(Node externs, Node root) {
    NodeTraversal.traverse(compiler, root, this);
    for (Entry> entry : Multimaps.asMap(functions).entrySet()) {
      Node addingRoot = compiler.getNodeForCodeInsertion(entry.getKey());
      List fnNodes = Lists.reverse(entry.getValue());
      if (!fnNodes.isEmpty()) {
        for (Node n : fnNodes) {
          Node nameNode = n.getFirstChild();
          String name = nameNode.getString();
          nameNode.setString("");
          addingRoot.addChildToFront(
              IR.var(IR.name(name), n).useSourceInfoIfMissingFromForTree(n));
          compiler.reportChangeToEnclosingScope(nameNode);
        }
        compiler.reportChangeToEnclosingScope(addingRoot);
      }
    }
  }

  @Override
  public boolean shouldTraverse(NodeTraversal t, Node n, Node parent) {
    Node grandparent = n.getAncestor(2);
    return grandparent == null || !grandparent.isScript();
  }

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    if (parent == null || !parent.isScript()) {
      return;
    }

    if (NodeUtil.isFunctionDeclaration(n)) {
      parent.removeChild(n);
      compiler.reportChangeToEnclosingScope(parent);

      functions.put(t.getModule(), n);
    }
  }
}