function polyfill() {
    var local = undefined;

    if (typeof global !== 'undefined') {
        local = global;
    } else if (typeof self !== 'undefined') {
        local = self;
    } else {
        try {
            local = Function('return this')();
        } catch (e) {
            throw new Error('polyfill failed because global object is unavailable in this environment');
        }
    }

    var P = local.Promise;

    if (P) {
        var promiseToString = null;
        try {
            promiseToString = Object.prototype.toString.call(P.resolve());
        } catch (e) {
            // silently ignored
        }

        if (promiseToString === '[object Promise]' && !P.cast) {
            return;
        }
    }

    local.Promise = Promise;
}
`catch` is simply sugar for `then(undefined, onRejection)` which makes it the same
    as the catch block of a try/catch statement.
  
    ```js
    function findAuthor(){
      throw new Error('couldn't find that author');
    }
  
    // synchronous
    try {
      findAuthor();
    } catch(reason) {
      // something went wrong
    }
  
    // async with promises
    findAuthor().catch(function(reason){
      // something went wrong
    });
    ```
  
    @method catch
    @param {Function} onRejection
    Useful for tooling.
    @return {Promise}