Syntax

JSObject *
JS_GetScopeChain(JSContext *cx);

Description

JS_GetScopeChain returns the first JSObject on the scope chain for the JavaScript code currently running in the given context, cx.

The ECMAScript standard, ECMA 262-3 §10, describes execution contexts and scope chains. A scope chain is a sequence of objects whose properties are searched whenever a script or function refers to a variable. These objects represent the lexical scope of the currently executing statement or expression, not the call stack, so they include:

• the variable objects of any enclosing functions or let statements or expressions, and any objects selected by enclosing with statements, in order from the most-nested scope outward;
• lastly the global object against which the function was created.

Note that cx's current global object, as set by JS_SetGlobalObject, is not guaranteed to be on the scope chain. If the currently executing function was created in the scope of a different global object, then that object will be the last object in the current scope chain. If the context is currently executing a script, and not in any function, it's running in a scope that was passed to JS_ExecuteScript or a similar function by the application. This scope chain may or may not contain cx's current global object.

If any code is currently executing in cx, JS_GetScopeChain returns a pointer to the first JSObject on the current scope chain. Otherwise, if cx has a global object, JS_GetScopeChain returns that. Otherwise, an error is reported and JS_GetScopeChain returns NULL.

To walk the scope chain, use JS_GetParent.

See Also

• MXR ID Search for JS_GetScopeChain
• JS_GetGlobalForScopeChain
• bug 632064