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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 2017 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.bundle;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtIncompatible;
import com.google.errorprone.annotations.Immutable;
import java.util.Optional;

/**
 * A source transformer for lowering JS language versions. May also include a runtime that needs to
 * be shipped with the final bundle.
 */
@GwtIncompatible
@Immutable
public class Transpiler extends CompilerBasedTransformer {

  private final String runtimeLibraryName;

  public Transpiler(CompilerBasedTransformer.CompilerSupplier compilerSupplier,
      String runtimeLibraryName) {
    super(compilerSupplier);
    this.runtimeLibraryName = checkNotNull(runtimeLibraryName);
  }

  public static CompilerBasedTransformer.CompilerSupplier compilerSupplier() {
    return new CompilerBasedTransformer.CompilerSupplier();
  }

  @Override
  public Optional getRuntime() {
    return Optional.of(runtimeLibraryName);
  }

  @Override
  public String getTranformationName() {
    return "Transpilation";
  }

  public static final Transpiler ES5_TRANSPILER =
      new Transpiler(new CompilerBasedTransformer.CompilerSupplier(), "es6_runtime");


  /** Recommended transpiler. */
  public static Transpiler toEs5() {
    return TO_ES5;
  }

  private static final Transpiler TO_ES5 =
      new Transpiler(new CompilerBasedTransformer.CompilerSupplier(), "es6_runtime");
}