Package org.mozilla.javascript

Class LambdaConstructor

java.lang.Object

org.mozilla.javascript.ScriptableObject

org.mozilla.javascript.IdScriptableObject

org.mozilla.javascript.BaseFunction

org.mozilla.javascript.LambdaFunction

org.mozilla.javascript.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:

• Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from class org.mozilla.javascript.ScriptableObject

ScriptableObject.KeyComparator

Field Summary

Fields

Modifier and Type	Field	Description
static final int	CONSTRUCTOR_DEFAULT	By default, the constructor may be invoked either way
static final int	CONSTRUCTOR_FUNCTION	If this flag is set, the constructor may be invoked as an ordinary function
static final int	CONSTRUCTOR_NEW	If this flag is set, the constructor may be invoked using "new"
protected final Constructable	targetConstructor

Fields inherited from class org.mozilla.javascript.LambdaFunction

target

Fields inherited from class org.mozilla.javascript.BaseFunction

Id_arguments, Id_arity, Id_length, Id_name, Id_prototype, MAX_INSTANCE_ID

Fields inherited from class org.mozilla.javascript.ScriptableObject

CONST, DONTENUM, EMPTY, PERMANENT, READONLY, UNINITIALIZED_CONST

Fields inherited from interface org.mozilla.javascript.Scriptable

NOT_FOUND

Constructor Summary

Constructors

Constructor	Description
LambdaConstructor(Scriptable scope, String name, int length, int flags, Constructable target)	Create a new function that may be used as a constructor.
LambdaConstructor(Scriptable scope, String name, int length, Callable target, Constructable targetConstructor)	Create a new function that may be used as a constructor.
LambdaConstructor(Scriptable scope, String name, int length, Constructable target)	Create a new function that may be used as a constructor.

Method Summary

Modifier and Type	Method	Description
Object	call(Context cx, Scriptable scope, Scriptable thisObj, Object[] args)	Should be overridden.
Scriptable	construct(Context cx, Scriptable scope, Object[] args)	Call the function as a constructor.
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.
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.
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.
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.
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.
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.
void	definePrototypeMethod(Scriptable scope, SymbolKey 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.
void	definePrototypeProperty(String name, Object value, int attributes)	Define a property that may be of any type on the prototype of this constructor.
void	definePrototypeProperty(Context cx, String name, Function<Scriptable,Object> getter, int attributes)	Define a property on the prototype using a function.
void	definePrototypeProperty(Context cx, String name, Function<Scriptable,Object> getter, BiConsumer<Scriptable,Object> setter, int attributes)	Define a property on the prototype using functions for getter and setter.
void	definePrototypeProperty(Symbol key, Object value, int attributes)

Methods inherited from class org.mozilla.javascript.LambdaFunction

getArity, getFunctionName, getLength

Methods inherited from class org.mozilla.javascript.BaseFunction

createObject, execIdCall, fillConstructorProperties, findInstanceIdInfo, findPrototypeId, getClassName, getClassPrototype, getInstanceIdName, getInstanceIdValue, getMaxInstanceId, getPrototypeProperty, getTypeOf, hasDefaultParameters, hasInstance, hasPrototypeProperty, initPrototypeId, isGeneratorFunction, setImmunePrototypeProperty, setInstanceIdAttributes, setInstanceIdValue, setPrototypeProperty, setPrototypePropertyAttributes, setStandardPropertyAttributes, setupDefaultPrototype

Methods inherited from class org.mozilla.javascript.IdScriptableObject

activatePrototypeMap, addIdFunctionProperty, defaultGet, defaultHas, defaultPut, defineOwnProperty, delete, delete, ensureType, ensureType, exportAsJSClass, findInstanceIdInfo, findPrototypeId, get, get, getAttributes, getAttributes, getOwnPropertyDescriptor, has, has, hasPrototypeMap, initPrototypeConstructor, initPrototypeMethod, initPrototypeMethod, initPrototypeMethod, initPrototypeValue, initPrototypeValue, instanceIdInfo, put, put, setAttributes

Methods inherited from class org.mozilla.javascript.ScriptableObject

applyDescriptorToAttributeBitset, associateValue, avoidObjectDetection, buildDataDescriptor, callMethod, callMethod, checkPropertyChange, checkPropertyDefinition, defineClass, defineClass, defineClass, defineConst, defineConstProperty, defineFunctionProperties, defineOwnProperties, defineOwnProperty, defineProperty, defineProperty, defineProperty, defineProperty, defineProperty, defineProperty, defineProperty, defineProperty, delete, deleteProperty, deleteProperty, ensureScriptable, ensureScriptableObject, ensureSymbolScriptable, equivalentValues, get, get, getAllIds, getArrayPrototype, getAssociatedValue, getAttributes, getAttributes, getAttributes, getClassPrototype, getDefaultValue, getDefaultValue, getExternalArrayData, getExternalArrayLength, getFunctionPrototype, getGeneratorFunctionPrototype, getGetterOrSetter, getGetterOrSetter, getIds, getObjectPrototype, getParentScope, getProperty, getProperty, getProperty, getPropertyIds, getPrototype, getTopLevelScope, getTopScopeValue, getTypedProperty, getTypedProperty, has, hasProperty, hasProperty, hasProperty, isAccessorDescriptor, isConst, isDataDescriptor, isEmpty, isExtensible, isFalse, isGenericDescriptor, isGetterOrSetter, isSealed, isTrue, preventExtensions, put, putConst, putConstProperty, putProperty, putProperty, putProperty, querySlot, redefineProperty, sameValue, sealObject, setAttributes, setAttributes, setAttributes, setAttributes, setCommonDescriptorProperties, setExternalArrayData, setGetterOrSetter, setParentScope, setPrototype, size

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface org.mozilla.javascript.Scriptable

delete, delete, get, get, getDefaultValue, getIds, getParentScope, getPrototype, has, has, put, put, setParentScope, setPrototype

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:

• Constant Field Values

CONSTRUCTOR_NEW

public static final int CONSTRUCTOR_NEW

If this flag is set, the constructor may be invoked using "new"

See Also:

• Constant Field Values

CONSTRUCTOR_DEFAULT

public static final int CONSTRUCTOR_DEFAULT

By default, the constructor may be invoked either way

See Also:

• Constant Field Values

targetConstructor

protected final transient Constructable targetConstructor

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. The new constructor function can be invoked using "new" or by calling it directly, and in either case will result in a new object being returned and wired to the correct prototype and 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 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. The "flags" argument controls whether the function may be invoked using "new," via a direct call, or both. If allowed by the flags, then the constructor will have the same effect either way. If not allowed by the flags, then a TypeError will be thrown.

Parameters:

scope - scope of the calling context

name - name of the function

length - the arity of the function

flags - which may be a combination of CONSTRUCTOR_NEW and CONSTRUCTOR_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,
 Callable target,
 Constructable targetConstructor)

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. The new constructor function will have different behavior depending on whether it is invoked via "new" or via a direct call. In the case of "new", a new object with a prototype and scope chain be returned, but in the case of a direct call, the user must implement whatever they need. This is typically used in the case of functions like the native Date constructor, which has totally different behavior depending on how it's invoked.

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.

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.

definePrototypeMethod

public void definePrototypeMethod(Scriptable scope,
 SymbolKey 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)

definePrototypeProperty

public void definePrototypeProperty(Context cx,
 String name,
 Function<Scriptable,Object> getter,
 int attributes)

Define a property on the prototype using a function. The function will be wired to a JavaScript function, so the resulting property will look just like one that was defined using "Object.defineOwnProperty" with a property descriptor.

definePrototypeProperty

public void definePrototypeProperty(Context cx,
 String name,
 Function<Scriptable,Object> getter,
 BiConsumer<Scriptable,Object> setter,
 int attributes)

Define a property on the prototype using functions for getter and setter. The function will be wired to a JavaScript function, so the resulting property will look just like one that was defined using "Object.defineOwnProperty" with a property descriptor.

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.