> Can someone explain to me what the difference really is between WASM and older tech like Java Applets, ActiveX, Silverlight and Macromedia Flash
As well as the security model differences other are debating, and WASM being an open standard that is easy to implement and under no control from a commercial entity, there is a significant difference in scope.
WebAssemply is just the runtime that executes byte-code compiled code efficiently. That's it. No large standard run-time (compile in everything you need), no UI manipulation (message passing to JS is how you affect the DOM, and how you ready DOM status back), etc. It odes one thing (crunch numbers, essentially) and does it well.
As well as the security model differences other are debating, and WASM being an open standard that is easy to implement and under no control from a commercial entity, there is a significant difference in scope.
WebAssemply is just the runtime that executes byte-code compiled code efficiently. That's it. No large standard run-time (compile in everything you need), no UI manipulation (message passing to JS is how you affect the DOM, and how you ready DOM status back), etc. It odes one thing (crunch numbers, essentially) and does it well.