extendscript-es5-shim/Object/isExtensible.js

a collection of useful es5-shims for Extendscript

// ES5 15.2.3.13
// http://es5.github.com/#x15.2.3.13
if (!Object.isExtensible) {
    Object.isExtensible = function isExtensible(object) {
        if (Object(object) !== object) {
            throw new TypeError('Object.isExtensible can only be called on Objects.');
        }
        return true;
    };
}