Class LambdaConstructor

All Implemented Interfaces:
Serializable, Callable, ConstProperties, Constructable, DebuggableObject, Function, IdFunctionCall, Scriptable, SymbolScriptable

public class LambdaConstructor extends LambdaFunction
This class implements a JavaScript function that may be used as a constructor by delegating to an interface that can be easily implemented as a lambda. The LambdaFunction class may be used to add functions to the prototype that are also implemented as lambdas.

In micro benchmarks (as of 2021) using this class to implement a built-in class is about 15% more efficient than using IdScriptableObject, and about 25% faster than using reflection via the ScriptableObject.defineClass() family of methods. Furthermore, it results in code that more directly maps to JavaScript idioms than either methods, it is much easier to implement than IdScriptableObject, and the lambda pattern makes it easier to maintain state in various ways that don't always map directly to the existing concepts.

See Also:
  • Field Details

    • CONSTRUCTOR_FUNCTION

      public static final int CONSTRUCTOR_FUNCTION
      If this flag is set, the constructor may be invoked as an ordinary function
      See Also:
    • CONSTRUCTOR_NEW

      public static final int CONSTRUCTOR_NEW
      If this flag is set, the constructor may be invoked using "new"
      See Also:
    • CONSTRUCTOR_DEFAULT

      public static final int CONSTRUCTOR_DEFAULT
      By default, the constructor may be invoked either way
      See Also:
  • Constructor Details

    • LambdaConstructor

      public LambdaConstructor(Scriptable scope, String name, int length, Constructable target)
      Create a new function that may be used as a constructor. The new object will have the Function prototype and no parent. The caller is responsible for binding this object to the appropriate scope.
      Parameters:
      scope - scope of the calling context
      name - name of the function
      length - the arity of the function
      target - an object that implements the function in Java. Since Constructable is a single-function interface this will typically be implemented as a lambda.
    • LambdaConstructor

      public LambdaConstructor(Scriptable scope, String name, int length, int flags, Constructable target)
      Create a new function and control whether it may be invoked using new, as a function, or both.
  • Method Details

    • call

      public Object call(Context cx, Scriptable scope, Scriptable thisObj, Object[] args)
      Description copied from class: BaseFunction
      Should be overridden.
      Specified by:
      call in interface Callable
      Specified by:
      call in interface Function
      Overrides:
      call in class LambdaFunction
      Parameters:
      cx - the current Context for this thread
      scope - the scope to execute the function relative to. This is set to the value returned by getParentScope() except when the function is called from a closure.
      thisObj - the JavaScript this object
      args - the array of arguments
      Returns:
      the result of the call
    • construct

      public Scriptable construct(Context cx, Scriptable scope, Object[] args)
      Description copied from interface: Function
      Call the function as a constructor.

      This method is invoked by the runtime in order to satisfy a use of the JavaScript new operator. This method is expected to create a new object and return it.

      Specified by:
      construct in interface Constructable
      Specified by:
      construct in interface Function
      Overrides:
      construct in class LambdaFunction
      Parameters:
      cx - the current Context for this thread
      scope - an enclosing scope of the caller except when the function is called from a closure.
      args - the array of arguments
      Returns:
      the allocated object
    • definePrototypeMethod

      public void definePrototypeMethod(Scriptable scope, String name, int length, Callable target)
      Define a function property on the prototype of the constructor using a LambdaFunction under the covers.
    • definePrototypeMethod

      public void definePrototypeMethod(Scriptable scope, String name, int length, Callable target, int attributes, int propertyAttributes)
      Define a function property on the prototype of the constructor using a LambdaFunction under the covers.
    • definePrototypeProperty

      public void definePrototypeProperty(String name, Object value, int attributes)
      Define a property that may be of any type on the prototype of this constructor.
    • definePrototypeProperty

      public void definePrototypeProperty(Symbol key, Object value, int attributes)
    • defineConstructorMethod

      public void defineConstructorMethod(Scriptable scope, String name, int length, Callable target, int attributes)
      Define a function property directly on the constructor that is implemented under the covers by a LambdaFunction.
      Parameters:
      name - the key to use to look up the new function property, and also the value to return for the "name" property of the Function object
      length - the value to return for the "length" property of the Function object
      target - the target to call when the method is invoked
      attributes - the attributes to set on the new property
    • defineConstructorMethod

      public void defineConstructorMethod(Scriptable scope, Symbol key, String name, int length, Callable target, int attributes)
      Define a function property directly on the constructor that is implemented under the covers by a LambdaFunction.
      Parameters:
      key - the Symbol to use to look up the property
      name - the value to return for the "name" property of the Function object
      length - the value to return for the "length" property of the Function object
      target - the target to call when the method is invoked
      attributes - the attributes to set on the new property
    • defineConstructorMethod

      public void defineConstructorMethod(Scriptable scope, String name, int length, Callable target, int attributes, int propertyAttributes)
      Define a function property directly on the constructor that is implemented under the covers by a LambdaFunction, and override the properties of its "name", "length", and "arity" properties.
    • convertThisObject

      public static <T> T convertThisObject(Scriptable thisObj, Class<T> targetClass)
      A convenience method to convert JavaScript's "this" object into a target class and throw a TypeError if it does not match. This is useful for implementing lambda functions, as "this" in JavaScript doesn't necessarily map to an instance of the class.