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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/. */
package org.mozilla.javascript;
import java.util.EnumMap;
/**
* A top-level scope object that provides special means to cache and preserve
* the initial values of the built-in constructor properties for better
* ECMAScript compliance.
*
* ECMA 262 requires that most constructors used internally construct
* objects with the original prototype object as value of their [[Prototype]]
* internal property. Since built-in global constructors are defined as
* writable and deletable, this means they should be cached to protect against
* redefinition at runtime.
*
* In order to implement this efficiently, this class provides a mechanism
* to access the original built-in global constructors and their prototypes
* via numeric class-ids. To make use of this, the new
* {@link ScriptRuntime#newBuiltinObject ScriptRuntime.newBuiltinObject} and
* {@link ScriptRuntime#setBuiltinProtoAndParent ScriptRuntime.setBuiltinProtoAndParent}
* methods should be used to create and initialize objects of built-in classes
* instead of their generic counterparts.
*
* Calling {@link org.mozilla.javascript.Context#initStandardObjects()}
* with an instance of this class as argument will automatically cache
* built-in classes after initialization. For other setups involving
* top-level scopes that inherit global properties from their proptotypes
* (e.g. with dynamic scopes) embeddings should explicitly call
* {@link #cacheBuiltins()} to initialize the class cache for each top-level
* scope.
*/
public class TopLevel extends IdScriptableObject {
static final long serialVersionUID = -4648046356662472260L;
/**
* An enumeration of built-in ECMAScript objects.
*/
public enum Builtins {
/** The built-in Object type. */
Object,
/** The built-in Array type. */
Array,
/** The built-in Function type. */
Function,
/** The built-in String type. */
String,
/** The built-in Number type. */
Number,
/** The built-in Boolean type. */
Boolean,
/** The built-in RegExp type. */
RegExp,
/** The built-in Error type. */
Error
}
private EnumMap ctors;
@Override
public String getClassName() {
return "global";
}
/**
* Cache the built-in ECMAScript objects to protect them against
* modifications by the script. This method is called automatically by
* {@link ScriptRuntime#initStandardObjects ScriptRuntime.initStandardObjects}
* if the scope argument is an instance of this class. It only has to be
* called by the embedding if a top-level scope is not initialized through
* initStandardObjects().
*/
public void cacheBuiltins() {
ctors = new EnumMap(Builtins.class);
for (Builtins builtin : Builtins.values()) {
Object value = ScriptableObject.getProperty(this, builtin.name());
if (value instanceof BaseFunction) {
ctors.put(builtin, (BaseFunction)value);
}
}
}
/**
* Static helper method to get a built-in object constructor with the given
* type from the given scope. If the scope is not
* an instance of this class or does have a cache of built-ins,
* the constructor is looked up via normal property lookup.
*
* @param cx the current Context
* @param scope the top-level scope
* @param type the built-in type
* @return the built-in constructor
*/
public static Function getBuiltinCtor(Context cx,
Scriptable scope,
Builtins type) {
// must be called with top level scope
assert scope.getParentScope() == null;
if (scope instanceof TopLevel) {
Function result = ((TopLevel)scope).getBuiltinCtor(type);
if (result != null) {
return result;
}
}
// fall back to normal constructor lookup
return ScriptRuntime.getExistingCtor(cx, scope, type.name());
}
/**
* Static helper method to get a built-in object prototype with the given
* type from the given scope. If the scope is not
* an instance of this class or does have a cache of built-ins,
* the prototype is looked up via normal property lookup.
*
* @param scope the top-level scope
* @param type the built-in type
* @return the built-in prototype
*/
public static Scriptable getBuiltinPrototype(Scriptable scope,
Builtins type) {
// must be called with top level scope
assert scope.getParentScope() == null;
if (scope instanceof TopLevel) {
Scriptable result = ((TopLevel)scope)
.getBuiltinPrototype(type);
if (result != null) {
return result;
}
}
// fall back to normal prototype lookup
return ScriptableObject.getClassPrototype(scope, type.name());
}
/**
* Get the cached built-in object constructor from this scope with the
* given type. Returns null if {@link #cacheBuiltins()} has not
* been called on this object.
* @param type the built-in type
* @return the built-in constructor
*/
public BaseFunction getBuiltinCtor(Builtins type) {
return ctors != null ? ctors.get(type) : null;
}
/**
* Get the cached built-in object prototype from this scope with the
* given type. Returns null if {@link #cacheBuiltins()} has not
* been called on this object.
* @param type the built-in type
* @return the built-in prototype
*/
public Scriptable getBuiltinPrototype(Builtins type) {
BaseFunction func = getBuiltinCtor(type);
Object proto = func != null ? func.getPrototypeProperty() : null;
return proto instanceof Scriptable ? (Scriptable) proto : null;
}
}