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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 2015 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.jscomp.NodeTraversal.AbstractPostOrderCallback;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;

/**
 * Shorten a object literal by using following features in ES6 upward:
 *   1. Shorthand assignment ({@code {a: a}} can be written as {@code {a}})
 *   2. Shorthand method ({@code {method: function(){}}} can be written
 *      as {@code {method(){}}})
 *
 */
class ObjectLitAssignmentShortening implements CompilerPass {

  private final AbstractCompiler compiler;

  ObjectLitAssignmentShortening(AbstractCompiler compiler) {
    this.compiler = compiler;
  }

  @Override
  public void process(Node externs, Node root) {
    NodeTraversal.traverseEs6(compiler, root, new ObjectLitShorteningCallback(compiler));
  }

  private static class ObjectLitShorteningCallback extends AbstractPostOrderCallback {

    AbstractCompiler compiler;

    ObjectLitShorteningCallback(AbstractCompiler compiler) {
      this.compiler = compiler;
    }

    @Override
    public void visit(NodeTraversal t, Node n, Node parent) {
      if (parent != null && parent.isObjectLit() && n.isStringKey()) {
        // Already object literal shorthand assignment
        if (!n.hasChildren()) {
          return;
        }

        Node valueNode = n.getFirstChild();
        if (valueNode.isName() && n.getString().equals(valueNode.getString())) {
          n.removeChild(valueNode);
          compiler.reportCodeChange();
        } else if (valueNode.isFunction() && !valueNode.isArrowFunction()) {
          // It is not worth rewriting the arrow function since even a return
          // statement is longer than the arrow function
          functionAssignmentShortening(n, valueNode, parent);
        }
      }
    }

    private void functionAssignmentShortening(
        Node n, Node functionNode, Node parent) {
      n.removeChild(functionNode);
      Node memDefNode = IR.memberFunctionDef(n.getString(), functionNode);
      parent.replaceChild(n, memDefNode);
      compiler.reportCodeChange();
    }
  }
}