Calling asm.js a subset of Javascript is a bit of a stretch. It looks nothing like idiomatic Javascript, and was more of a low-level statically-typed language d

Calling asm.js a subset of Javascript is a bit of a stretch. It looks nothing like idiomatic Javascript, and was more of a low-level statically-typed language dressed up in Javascript clothing. At some point they realized that representing this low-level code as Javascript text instead of as specially-designed bytecode added a significant ammount of parsing and compilation overhead, which was one of the initial motivations for the creation of WebAssembly. If I had to sum up WASM in one sentence, it is that it is kind of like the JVM, except that its instruction set was designed specifically for running programs downloaded from the web. Special attention was paid to security and startup latency.