Google, Microsoft, Mozilla and  WebKit project engineers  announced that they have teamed up to launch WebAssembly, a new binary format for compiling applications for the web. They all have joined hands to create code for use in future web browsers that promises up to 20 times faster speed.

Now the web has its own standard , for better or worse javascript is it’s language. There are many projects whose purpose is to speeding up javascript  (like Mozilla’s asm.js project). Now all these type of projects come together in the form of WebAssembly(or wasm in short).

What is WebAssembly ?

Dubbed WebAssembly , a project to portable create byte-code for the web that will be more efficient for both Desktop and Mobile web browsers.
As we all know bytecode is machine level language . Any code of high-level languages such as C/C++, Java, Ruby etc first converted into bytecode before executing. Even there are many steps involving in converting a C program into an executable form. You can see them here .
That’s why they are using bytecode to create web browser that will be faster than other ones to load.  Mostly javascript is uses in web to handle request and by default javascript engine compiles the downloaded javascript files.
However, improvements have been made to load times via Asm.js — the stripped-down JavaScript dialect described as an “assembly language for the web”— but bytecode-based systems such as .NET are faster and enable efficient compilation.

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20% Faster Performance

It is obvious that assembly is faster than higher level language such as javascript, as it is more closer to machine level. You can see here how it works .
Mozilla developer said:-

"I'm happy to report that we at Mozilla have started working with Chromium, Edge and WebKit engineers 
on creating a new standard, WebAssembly," said Mozilla developer Luke Wagner, "that defines a portable,
size- and load-time-efficient format and execution model specifically designed to serve as a compilation target for the Web."

Currently only C/C++ code can compiled into webassembly (wasm) file ,Instead of having to parse the full code, though, which can often take quite a while (especially on mobile), WebAssembly can be decoded significantly faster.
It’s not often that we see all the major browser vendors work together on a project like this, so this is definitely something worth watching in the months and years ahead.