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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 2011 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.javascript.rhino.Node;
import com.google.javascript.rhino.Token;

/**
 * Reorder constant expression hoping for a better compression.
 * ex. x === 0 -> 0 === x
 * After reordering, expressions like 0 === x and 0 === y may have higher
 * compression together than their original counterparts.
 */
class PeepholeReorderConstantExpression extends AbstractPeepholeOptimization {

  @Override
  Node optimizeSubtree(Node subtree) {
    // if the operator is symmetric
    if (NodeUtil.isSymmetricOperation(subtree)
        || NodeUtil.isRelationalOperation(subtree)) {
      if (NodeUtil.precedence(subtree.getToken())
          == NodeUtil.precedence(subtree.getFirstChild().getToken())) {
        // then flipping would add parens
        return subtree;
      }
      // right value is immutable and left is not
      if (NodeUtil.isImmutableValue(subtree.getLastChild())
          && !NodeUtil.isImmutableValue(subtree.getFirstChild())) {

        // if relational, get the inverse operator.
        if (NodeUtil.isRelationalOperation(subtree)){
          Token inverseOperator = NodeUtil.getInverseOperator(subtree.getToken());
          subtree.setToken(inverseOperator);
        }

        // swap them
        Node firstNode = subtree.removeFirstChild();
        Node lastNode = subtree.getLastChild().detach();

        subtree.addChildToFront(lastNode);
        subtree.addChildToBack(firstNode);
        reportChangeToEnclosingScope(subtree);
      }
    }
    return subtree;
  }
}