QJSValue

QJSValue is a value type in Qt that represents a JavaScript value within the Qt JavaScript engine (QJSEngine). It can hold JavaScript primitives such as undefined, null, boolean, number, and string, as well as objects, arrays, and functions. A QJSValue can therefore model any value that can be manipulated from within JavaScript, including complex objects created or exposed from C++.

A key aspect of QJSValue is its type inspection and conversion capabilities. It provides predicates such as isUndefined, isNull, isBool, isNumber, isString, isObject, and isFunction to determine the stored type. It can convert to native C++ or Qt types through methods like toBool, toDouble, toString, and toVariant. Conversely, values can be constructed from C++ data using helpers such as fromVariant, and JavaScript values can be converted back to QVariant for use in C++ code. Objects and arrays are accessed through property and setProperty, and can be interrogated with hasProperty or related operations.

If the value represents a JavaScript function, it can be invoked from C++ with a specified this object and a list of arguments. QJSValue also integrates with QJSEngine for object bridging: C++ objects (QObject-based) can be exposed to JavaScript through engine-provided mechanisms (for example, creating a JavaScript proxy with newQObject). This enables calling C++ slots or accessing signals from JavaScript, and vice versa.

Lifecycle and usage notes: QJSValue is a lightweight handle whose semantics are tied to the owning QJSEngine. It is commonly used to pass data between C++ and JavaScript, evaluate scripts, and implement bindings between the two environments. Arrays and complex objects are typically represented as QJSValue objects with object semantics, not separate array types.