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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.

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/*
 * Copyright 2014 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 static com.google.javascript.jscomp.Es6ToEs3Util.createType;
import static com.google.javascript.jscomp.Es6ToEs3Util.withType;

import com.google.common.base.Supplier;
import com.google.common.base.Suppliers;
import com.google.javascript.jscomp.AbstractCompiler.MostRecentTypechecker;
import com.google.javascript.jscomp.parsing.parser.FeatureSet;
import com.google.javascript.jscomp.parsing.parser.FeatureSet.Feature;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.TypeI;
import com.google.javascript.rhino.jstype.JSTypeNative;

/**
 * Converts ES7 code to valid ES6 code.
 *
 * Currently this class converts ** and **= operators to calling Math.pow
 */
public final class Es7ToEs6Converter implements NodeTraversal.Callback, HotSwapCompilerPass {
  private final AbstractCompiler compiler;
  private static final FeatureSet transpiledFeatures =
      FeatureSet.BARE_MINIMUM.with(Feature.EXPONENT_OP);
  private final boolean addTypes;
  private final Supplier mathPow = Suppliers.memoize(new MathPowSupplier());

  public Es7ToEs6Converter(AbstractCompiler compiler) {
    this.compiler = compiler;
    this.addTypes = MostRecentTypechecker.NTI.equals(compiler.getMostRecentTypechecker());
  }

  @Override
  public void process(Node externs, Node root) {
    TranspilationPasses.processTranspile(compiler, externs, transpiledFeatures, this);
    TranspilationPasses.processTranspile(compiler, root, transpiledFeatures, this);
    TranspilationPasses.markFeaturesAsTranspiledAway(compiler, transpiledFeatures);
  }

  @Override
  public void hotSwapScript(Node scriptRoot, Node originalRoot) {
    TranspilationPasses.hotSwapTranspile(compiler, scriptRoot, transpiledFeatures, this);
    TranspilationPasses.markFeaturesAsTranspiledAway(compiler, transpiledFeatures);
  }

  @Override
  public boolean shouldTraverse(NodeTraversal t, Node n, Node parent) {
    return true;
  }

  @Override
  public void visit(NodeTraversal t, Node n, Node parent) {
    switch (n.getToken()) {
      case EXPONENT:
        visitExponentiationExpression(n, parent);
        break;
      case ASSIGN_EXPONENT:
        visitExponentiationAssignmentExpression(n, parent);
        break;
      default:
        break;
    }
  }

  private void visitExponentiationExpression(Node n, Node parent) {
    Node left = n.removeFirstChild();
    Node right = n.removeFirstChild();
    Node mathDotPowCall =
        withType(IR.call(mathPow.get().cloneTree(), left, right), n.getTypeI())
            .useSourceInfoIfMissingFromForTree(n);
    parent.replaceChild(n, mathDotPowCall);
    compiler.reportChangeToEnclosingScope(mathDotPowCall);
  }

  private void visitExponentiationAssignmentExpression(Node n, Node parent) {
    Node left = n.removeFirstChild();
    Node right = n.removeFirstChild();
    Node mathDotPowCall =
        withType(IR.call(mathPow.get().cloneTree(), left.cloneTree(), right), n.getTypeI());
    Node assign =
        withType(IR.assign(left, mathDotPowCall), n.getTypeI())
            .useSourceInfoIfMissingFromForTree(n);
    parent.replaceChild(n, assign);
    compiler.reportChangeToEnclosingScope(assign);
  }

  private class MathPowSupplier implements Supplier {
    @Override public Node get() {
      Node n = NodeUtil.newQName(compiler, "Math.pow");
      if (addTypes) {
        TypeI mathType = compiler.getTypeIRegistry().getGlobalType("Math");
        TypeI mathPowType = mathType.toMaybeObjectType().getPropertyType("pow");
        TypeI stringType =
            createType(addTypes, compiler.getTypeIRegistry(), JSTypeNative.STRING_TYPE);
        n.setTypeI(mathPowType);
        n.getFirstChild().setTypeI(mathType);
        n.getSecondChild().setTypeI(stringType);
      }
      return n;
    }
  }
}