a view from prog lang perspective, a good article
Understand WebAssembly: Why It Will Change the Web - Strumenta
In practical terms, WebAssembly is implemented by browsers’ developers on the back of the existing JavaScript engine. Essentially, it is designed to substitute JavaScript as the destination of compilers and transpilers on the web. For instance, instead of compiling TypeScript to JavaScript, its developers could now compile to WebAssembly. In short, it is not a new virtual machine, it is a new format for the same JavaScript VM that is included in every browser. This will make possible to take advantage of the existing JavaScript infrastructure, without using JavaScript.