pub unsafe extern "C" fn JS_IsExtensible(
    cx: *mut JSContext,
    obj: HandleObject,
    extensible: *mut bool
) -> bool
Expand description

Determine whether obj is extensible. Extensible objects can have new properties defined on them. Inextensible objects can’t, and their [[Prototype]] slot is fixed as well.

Implements: ES6 [[IsExtensible]] internal method.