Today the browsers virtual machines can work only with Javascript code. That means that if you want to use another language you have to convert in to Javascript

Today the browsers virtual machines can work only with Javascript code. That means that if you want to use another language you have to convert in to Javascript, and you are obviously limited by the features of Javascript. The goal of WASM is to provide a language similar to Assembly (or bytecode of Java) that can be understood by the virtual machines of browser, and so to have a new way to compile languages and use them in the browsers. WASM can also be optimized better, having more features than Javascript (for example javascript uses only double as number types, while WASM has integers and floats)