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I need to find out at runtime if a variable of type any implements an interface. How to find out at runtime if a variable of type any implements an interface? Email me at this address if a comment is added after mine: Email me if a comment is added after mine. I understand that javascript as a dynamic language has no concept of interfaces. Describe how an object should look This question is the direct analogon to Class type check with TypeScript. How can I use it ? But that isn't true, the name does exist in the current scope. If you enter this code in the typescript playground, the last line will be marked as an error, "The name A does not exist in the current scope". I wondered how the type A could vanish like that but a look at the generated javascript explains the problem: There is no representation of A as an interface, therefore no runtime type checks are possible. Ltd. All rights Reserved. Is there any way to type check for interfaces? I can even change the variable declaration to var a:A={member:"foobar"}; without complaints from the editor. Why typescript complains that XXX is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint X? When do you use them? What's the difference between class and interface in TypeScript? (y as READ MORE, If you want a key/value data structure READ MORE, Interfaces Is there any way to type check for interfaces? After browsing the web and finding the other question on SO I changed the interface to a class but then I can't use object literals to create instances. How to set meta tags using Angular universal SSR and ngx-seo plug-in? The typescript playground's autocompletion reveals that typescript even offers a method implements. Email me at this address if my answer is selected or commented on: Email me if my answer is selected or commented on, Typescript open-api cilent generation and usage of `fetch`.