CopperSpice API  1.7.2
QScriptContext Class Reference

The QScriptContext class represents a CsScript function invocation. More...

Public Types

enum  Error
 
enum  ExecutionState
 

Public Methods

 ~QScriptContext ()
 
QScriptValue activationObject () const
 
QScriptValue argument (int index) const
 
int argumentCount () const
 
QScriptValue argumentsObject () const
 
QStringList backtrace () const
 
QScriptValue callee () const
 
QScriptEngineengine () const
 
bool isCalledAsConstructor () const
 
QScriptContext * parentContext () const
 
void setActivationObject (const QScriptValue &activation)
 
void setThisObject (const QScriptValue &thisObject)
 
ExecutionState state () const
 
QScriptValue thisObject () const
 
QScriptValue throwError (const QString &text)
 
QScriptValue throwError (Error error, const QString &text)
 
QScriptValue throwValue (const QScriptValue &value)
 
QString toString () const
 

Detailed Description

The QScriptContext class represents a CsScript function invocation.

A QScriptContext provides access to the ‘this’ object and arguments passed to a script function. You typically want to access this information when you are writing a native (C++) function (see QScriptEngine::newFunction()) that will be called from script code. For example, when the script code.

foo(20.5, "hello", new Object())

is evaluated, a QScriptContext will be created, and the context will carry the arguments as QScriptValues; in this particular case, the arguments will be one QScriptValue containing the number 20.5, a second QScriptValue containing the string "hello", and a third QScriptValue containing a CsScript object.

Use argumentCount() to get the number of arguments passed to the function, and argument() to get an argument at a certain index. The argumentsObject() function returns a CsScript array object containing all the arguments; you can use the QScriptValueIterator to iterate over its elements, or pass the array on as arguments to another script function using QScriptValue::call().

Use thisObject() to get the ‘this’ object associated with the function call, and setThisObject() to set the ‘this’ object. If you are implementing a native "instance method", you typically fetch the thisObject() and access one or more of its properties:

QScriptValue Person_prototype_fullName(QScriptContext *context, QScriptEngine *engine)
{
QScriptValue self = context->thisObject();
QString result;
result += self.property("firstName").toString();
result += " ";
result += self.property("lastName").toString();
return result;
}

Use isCalledAsConstructor() to determine if the function was called as a constructor (e.g. "new foo()" (as constructor) or just "foo()"). When a function is called as a constructor, the thisObject() contains the newly constructed object that the function is expected to initialize.

Use throwValue() or throwError() to throw an exception.

Use callee() to obtain the QScriptValue that represents the function being called. This can for example be used to call the function recursively.

Use parentContext() to get a pointer to the context that precedes this context in the activation stack. This is mostly useful for debugging purposes (e.g. when constructing some form of backtrace).

The activationObject() function returns the object that is used to hold the local variables associated with this function call. You can replace the activation object by calling setActivationObject(). A typical usage of these functions is when you want script code to be evaluated in the context of the parent context, e.g. to implement an include() function:

{
QString fileName = ctx->argument(0).toString();
QString contents = readTheFile(fileName);
return eng->evaluate(contents, fileName);
}

Use backtrace() to get a human-readable backtrace associated with this context. This can be useful for debugging purposes when implementing native functions. The toString() function provides a string representation of the context. (QScriptContextInfo provides more detailed debugging-related information about the QScriptContext.)

Use engine() to obtain a pointer to the QScriptEngine that this context resides in.

See also
QScriptContextInfo, QScriptEngine::newFunction(), QScriptable

Member Enumeration Documentation

This enum specifies types of error.

ConstantValueDescription
QScriptContext::ReferenceError1A reference error.
QScriptContext::SyntaxError2A syntax error.
QScriptContext::TypeError3A type error.
QScriptContext::RangeError4A range error.
QScriptContext::URIError5A URI error.
QScriptContext::UnknownError0An unknown error.

This enum specifies the execution state of the context.

ConstantValueDescription
QScriptContext::NormalState0The context is in a normal state.
QScriptContext::ExceptionState1The context is in an exceptional state.

Constructor & Destructor Documentation

QScriptContext::~QScriptContext ( )

Destroys this QScriptContext.

Method Documentation

QScriptValue QScriptContext::activationObject ( ) const

Returns the activation object of this QScriptContext. The activation object provides access to the local variables associated with this context.

Note
The activation object might not be available if there is no active QScriptEngineAgent, as it might be optimized.
See also
setActivationObject(), argument(), argumentsObject()
QScriptValue QScriptContext::argument ( int  index) const

Returns the function argument at the given index.

If index >= argumentCount(), a QScriptValue of the primitive type Undefined is returned.

See also
argumentCount()
int QScriptContext::argumentCount ( ) const

Returns the number of arguments passed to the function in this invocation.

Note that the argument count can be different from the formal number of arguments (the length property of callee()).

See also
argument()
QScriptValue QScriptContext::argumentsObject ( ) const

Returns the arguments object of this QScriptContext.

The arguments object has properties callee (equal to callee()) and length (equal to argumentCount()), and properties 0, 1, ..., argumentCount() - 1 that provide access to the argument values. Initially, property P (0 <= P < argumentCount()) has the same value as argument(P). In the case when P is less than the number of formal parameters of the function, P shares its value with the corresponding property of the activation object (activationObject()). This means that changing this property changes the corresponding property of the activation object and vice versa.

See also
argument(), activationObject()
QStringList QScriptContext::backtrace ( ) const

Returns a human-readable backtrace of this QScriptContext.

Each line is of the form <function-name>(<arguments>)&lt;file-name>:<line-number>.

To access individual pieces of debugging-related information (for example, to construct your own backtrace representation), use QScriptContextInfo.

See also
QScriptEngine::uncaughtExceptionBacktrace(), QScriptContextInfo, toString()
QScriptValue QScriptContext::callee ( ) const

Returns the callee. The callee is the function object that this QScriptContext represents an invocation of.

QScriptEngine * QScriptContext::engine ( ) const

Returns the QScriptEngine that this QScriptContext belongs to.

bool QScriptContext::isCalledAsConstructor ( ) const

Returns true if the function was called as a constructor (e.g. "new foo()"), otherwise returns false.

When a function is called as constructor, the thisObject() contains the newly constructed object to be initialized.

Note
This function is only guaranteed to work for a context corresponding to native functions.
QScriptContext * QScriptContext::parentContext ( ) const

Returns the parent context of this QScriptContext.

void QScriptContext::setActivationObject ( const QScriptValue activation)

Sets the activation object of this QScriptContext to be the given activation.

If activation is not an object, this function does nothing.

Note
For a context corresponding to a JavaScript function, this is only guaranteed to work if there was an QScriptEngineAgent active on the engine while the function was evaluated.
See also
activationObject()
void QScriptContext::setThisObject ( const QScriptValue thisObject)

Sets the ‘this’ object associated with this QScriptContext to be thisObject.

If thisObject is not an object, this function does nothing.

See also
thisObject()
ExecutionState QScriptContext::state ( ) const

Returns the execution state of this QScriptContext.

QScriptValue QScriptContext::thisObject ( ) const

Returns the ‘this’ object associated with this QScriptContext.

See also
setThisObject()
QScriptValue QScriptContext::throwError ( const QString text)

Throws an error with the given text. Returns the created error object.

See also
throwValue(), state()
QScriptValue QScriptContext::throwError ( Error  error,
const QString text 
)

Throws an error with the given text. Returns the created error object.

The text will be stored in the message property of the error object.

The error object will be initialized to contain information about the location where the error occurred; specifically, it will have properties lineNumber, fileName and stack. These properties are described in CsScript Extensions to ECMAScript.

See also
throwValue(), state()
QScriptValue QScriptContext::throwValue ( const QScriptValue value)

Throws an exception with the given value. Returns the value thrown (the same as the argument).

See also
throwError(), state()
QString QScriptContext::toString ( ) const

Returns a string representation of this context. This is useful for debugging.

See also
backtrace()