篡改任意对象方法,来监视方法被调用

function WatchMetod(obj, method, before, after) {
      obj[‘_‘ + method] = obj[method];
      obj[method] = function () {
        var args = [], len = arguments.length;
        while (len--) args[len] = arguments[len];
        before(args);
        var result = obj[‘_‘ + method].apply(this, args);
        after(args, result);
        return result;
      }
    }