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Creating Extension Methods Using Typescript using decorators. C#'s extension method feature is a work around. We are adding the the function to the prototype of the passed in class. This trick will not work on most third party libraries assuming that they are safeguarded against prototype pollution. The beauty of extension methods is that it should work on classes that we don't have any control over. So this trick won't work on the most third-party libraries. (https://stackblitz.com/cms/TypeScript/issues/9)