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Rhino is an open-source implementation of JavaScript written entirely in Java. It is typically embedded into Java applications to provide scripting to end users.
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/* -*- Mode: java; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

// API class

package org.mozilla.javascript;

public interface ConstProperties {
    /**
     * Sets a named const property in this object.
     *
     * The property is specified by a string name as defined for Scriptable.get.
     *
     * 
The possible values that may be passed in are as defined for Scriptable.get.
     * A class that implements this method may choose to ignore calls to set certain properties, in
     * which case those properties are effectively read-only.
     *
     * 
For properties defined in a prototype chain, use putProperty in
     * ScriptableObject.
     *
     * 
Note that if a property a is defined in the prototype p of an object
     * o, then evaluating o.a = 23 will cause set to be called on
     * the prototype p with o as the start parameter. To preserve JavaScript
     * semantics, it is the Scriptable object's responsibility to modify o.
     *
     * 
This design allows properties to be defined in prototypes and implemented in terms of
     * getters and setters of Java values without consuming slots in each instance.
     *
     * 
The values that may be set are limited to the following:
     *
     * 

     *   java.lang.Boolean objects
     *   
java.lang.String objects
     *   
java.lang.Number objects
     *   
org.mozilla.javascript.Scriptable objects
     *   
null
     *   
The value returned by Context.getUndefinedValue()
     * 
     *
     * Arbitrary Java objects may be wrapped in a Scriptable by first calling 
     * Context.toObject. This allows the property of a JavaScript object to contain an
     * arbitrary Java object as a value.
     *
     * Note that has will be called by the runtime first before set is
     * called to determine in which object the property is defined. Note that this method is not
     * expected to traverse the prototype chain, which is different from the ECMA [[Put]] operation.
     *
     * @param name the name of the property
     * @param start the object whose property is being set
     * @param value value to set the property to
     * @see org.mozilla.javascript.Scriptable#has(String, Scriptable)
     * @see org.mozilla.javascript.Scriptable#get(String, Scriptable)
     * @see org.mozilla.javascript.ScriptableObject#putProperty(Scriptable, String, Object)
     * @see org.mozilla.javascript.Context#toObject(Object, Scriptable)
     */
    public void putConst(String name, Scriptable start, Object value);

    /**
     * Reserves a definition spot for a const. This will set up a definition of the const property,
     * but set its value to undefined. The semantics of the start parameter is the same as for
     * putConst.
     *
     * @param name The name of the property.
     * @param start The object whose property is being reserved.
     */
    public void defineConst(String name, Scriptable start);

    /**
     * Returns true if the named property is defined as a const on this object.
     *
     * @param name
     * @return true if the named property is defined as a const, false otherwise.
     */
    public boolean isConst(String name);
}