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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 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.parsing.parser;

import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Maps;
import java.util.EnumMap;

/**
 * The JavaScript keywords.
 */
public enum Keywords {

    // 7.6.1.1 Keywords
    BREAK("break", TokenType.BREAK),
    CASE("case", TokenType.CASE),
    CATCH("catch", TokenType.CATCH),
    CONTINUE("continue", TokenType.CONTINUE),
    DEBUGGER("debugger", TokenType.DEBUGGER),
    DEFAULT("default", TokenType.DEFAULT),
    DELETE("delete", TokenType.DELETE),
    DO("do", TokenType.DO),
    ELSE("else", TokenType.ELSE),
    FINALLY("finally", TokenType.FINALLY),
    FOR("for", TokenType.FOR),
    FUNCTION("function", TokenType.FUNCTION),
    IF("if", TokenType.IF),
    IN("in", TokenType.IN),
    INSTANCEOF("instanceof", TokenType.INSTANCEOF),
    NEW("new", TokenType.NEW),
    RETURN("return", TokenType.RETURN),
    SWITCH("switch", TokenType.SWITCH),
    THIS("this", TokenType.THIS),
    THROW("throw", TokenType.THROW),
    TRY("try", TokenType.TRY),
    TYPEOF("typeof", TokenType.TYPEOF),
    VAR("var", TokenType.VAR),
    VOID("void", TokenType.VOID),
    WHILE("while", TokenType.WHILE),
    WITH("with", TokenType.WITH),

    // 7.6.1.2 Future Reserved Words
    CLASS("class", TokenType.CLASS),
    CONST("const", TokenType.CONST),
    ENUM("enum", TokenType.ENUM),
    EXPORT("export", TokenType.EXPORT),
    EXTENDS("extends", TokenType.EXTENDS),
    IMPORT("import", TokenType.IMPORT),
    SUPER("super", TokenType.SUPER),

    // Future Reserved Words in a strict context
    IMPLEMENTS("implements", TokenType.IMPLEMENTS),
    INTERFACE("interface", TokenType.INTERFACE),
    LET("let", TokenType.LET),
    PACKAGE("package", TokenType.PACKAGE),
    PRIVATE("private", TokenType.PRIVATE),
    PROTECTED("protected", TokenType.PROTECTED),
    PUBLIC("public", TokenType.PUBLIC),
    STATIC("static", TokenType.STATIC),
    YIELD("yield", TokenType.YIELD),

    //7.8 Literals
    NULL("null", TokenType.NULL),
    TRUE("true", TokenType.TRUE),
  FALSE("false", TokenType.FALSE);

  private static final ImmutableMap KEYWORDS_BY_NAME;
  private static final ImmutableMap KEYWORDS_BY_TYPE;

  static {
    ImmutableMap.Builder keywordsByName = ImmutableMap.builder();
    EnumMap keywordsByType = new EnumMap<>(TokenType.class);
    for (Keywords kw : Keywords.values()) {
      keywordsByName.put(kw.value, kw);
      keywordsByType.put(kw.type, kw);
    }
    KEYWORDS_BY_NAME = keywordsByName.buildOrThrow();
    KEYWORDS_BY_TYPE = Maps.immutableEnumMap(keywordsByType);
  }

  public final String value;
  public final TokenType type;

  Keywords(String value, TokenType type) {
    this.value = value;
    this.type = type;
  }

  @Override
  public String toString() {
    return value;
  }

  public static boolean isKeyword(String value) {
    return get(value) != null;
  }

  public static boolean isKeyword(TokenType token) {
    return get(token) != null;
  }

  /**
   * Returns true if {@code token} is a "future reserved word" which can
   * be used as a variable identifier, but only in non-strict mode.
   */
  public static boolean isStrictKeyword(TokenType token) {
    switch(token) {
      case IMPLEMENTS:
      case INTERFACE:
      case LET:
      case PACKAGE:
      case PRIVATE:
      case PROTECTED:
      case PUBLIC:
      case STATIC:
      case YIELD:
        return true;
      default:
        return false;
    }
  }

  public static TokenType getTokenType(String value) {
    return KEYWORDS_BY_NAME.get(value).type;
  }

  public static Keywords get(String value) {
    return KEYWORDS_BY_NAME.get(value);
  }

  public static Keywords get(TokenType token) {
    return KEYWORDS_BY_TYPE.get(token);
  }
}