Package org.mozilla.javascript

Class TopLevel

  • All Implemented Interfaces:
    java.io.Serializable, ConstProperties, DebuggableObject, IdFunctionCall, Scriptable
    Direct Known Subclasses:
    ImporterTopLevel, ModuleScope
    public class TopLevel
extends IdScriptableObject
    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 ScriptRuntime.newBuiltinObject and ScriptRuntime.setBuiltinProtoAndParent methods should be used to create and initialize objects of built-in classes instead of their generic counterparts.

    Calling 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 cacheBuiltins() to initialize the class cache for each top-level scope.

    See Also:
    Serialized Form

    • Constructor Detail

      • TopLevel

        public TopLevel()

    • Method Detail

      • getClassName

        public java.lang.String getClassName()
        Description copied from class: ScriptableObject
        Return the name of the class. This is typically the same name as the constructor. Classes extending ScriptableObject must implement this abstract method.
        Specified by:
        getClassName in interface Scriptable
        Specified by:
        getClassName in class ScriptableObject

      • cacheBuiltins

        public void cacheBuiltins()
        Cache the built-in ECMAScript objects to protect them against modifications by the script. This method is called automatically by 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().

      • getBuiltinCtor

        public static Function getBuiltinCtor​(Context cx,
                                      Scriptable scope,
                                      TopLevel.Builtins type)
        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.
        Parameters:
        cx - the current Context
        scope - the top-level scope
        type - the built-in type
        Returns:
        the built-in constructor

      • getBuiltinPrototype

        public static Scriptable getBuiltinPrototype​(Scriptable scope,
                                             TopLevel.Builtins type)
        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.
        Parameters:
        scope - the top-level scope
        type - the built-in type
        Returns:
        the built-in prototype

      • getBuiltinCtor

        public BaseFunction getBuiltinCtor​(TopLevel.Builtins type)
        Get the cached built-in object constructor from this scope with the given type. Returns null if cacheBuiltins() has not been called on this object.
        Parameters:
        type - the built-in type
        Returns:
        the built-in constructor

      • getBuiltinPrototype

        public Scriptable getBuiltinPrototype​(TopLevel.Builtins type)
        Get the cached built-in object prototype from this scope with the given type. Returns null if cacheBuiltins() has not been called on this object.
        Parameters:
        type - the built-in type
        Returns:
        the built-in prototype