JavaScript® (often shortened to JS) is a lightweight, interpreted, object-oriented language with first-class functions, most known as the scripting language for Web pages, but used in many non-browser environments as well such as node.js or Apache CouchDB. It is a prototype-based, multi-paradigm scripting language that is dynamic, and supports object-oriented, imperative, and functional programming styles.

javascript

This course begins with some small steps for working with WebAssembly straight away using online tools wasm Explorer and wasm Fiddle to try out the examples in the browser. We start by calling a WebAssembly function from JS, then a JS function from WebAssembly, then go on to reading and writing WebAssembly memory from JS. To move beyond these online sandboxes, we show the exact steps for setting up and running a complete local WebAssembly build workflow using the experimental LLVM WebAssembly build target. We then take a demo WebGL application written in JS and show how we can optimize this with WebAssembly to get a real world example of a WebAssembly performance improvement, although it isn’t as obvious a process as we might have hoped.

In this introduction, we show a simple WebAssembly function that returns the square root of a number. To create this function we load up WebAssembly Explorer (https://mbebenita.github.io/WasmExplorer/), writing the native WAST code to create and export the function. We compile and download the resulting WebAssembly binary, loading this with the Fetch API and WebAssembly JavaScript API to call the function in the browser.

Demo Repo: https://github.com/guybedford/wasm-intro

Create and Run a Native WebAssembly Function

We use the C language instead of pure WAST to create a square root function using WASM Fiddle (https://wasdk.github.io/WasmFiddle//). We show how to run the WebAssembly in WASM Fiddle, then download and run it in the browser using a helper function to load the WebAssembly.

WASM Fiddle: https://wasdk.github.io/WasmFiddle/?t96rp

Demo Repo: https://github.com/guybedford/wasm-intro

Compile C Code into WebAssembly

Using WASM Fiddle, we show how to write a simple number logger function that calls a consoleLog function defined in JavaScript. We then download and run the same function in a local project.

WASM Fiddle: https://wasdk.github.io/WasmFiddle/?cvrmt

Demo Repo: https://github.com/guybedford/wasm-intro

Call a JavaScript Function from WebAssembly

We use an offset exporting function to get the address of a string in WebAssembly memory. We then create a typed array on top of the WebAssembly memory representing the raw string data, and decode that into a JavaScript string.

WASM Fiddle: https://wasdk.github.io/WasmFiddle/?6wzgh

Demo Repo: https://github.com/guybedford/wasm-intro

Read WebAssembly Memory from JavaScript

We write a function that converts a string to lowercase in WebAssembly, demonstrating how to set the input string from JavaScript.

WASM Fiddle: https://wasdk.github.io/WasmFiddle/?h1s69

Demo Repo: https://github.com/guybedford/wasm-intro

Write to WebAssembly Memory from JavaScript

We demonstrate how to build a WebAssembly module that depends on malloc, linking in a pre-built malloc implementation at runtime, using a JS binding trick to handle the circular reference between the two WebAssembly modules. We then optimize the load process to ensure we are fetching these modules in parallel.

Malloc implementation: https://github.com/guybedford/wasm-stdlib-hack/blob/master/dist/memory.wasm

WASM Fiddle: https://wasdk.github.io/WasmFiddle/?1feerp

Demo Repo: https://github.com/guybedford/wasm-intro

Allocate Dynamic Memory in WebAssembly with Malloc

Starting from the previous example, we rebuild the program code to import its memory instead of exporting it. We then use this to simplify the application loading code.

Emscripten: https://kripken.github.io/emscripten-site/

Demo Repo: https://github.com/guybedford/wasm-intro

Create and Import a WebAssembly Memory

We go through the command-line steps to compile C/C++ via LLVM into an intermediate S file, then use Binaryen to compile that S file into a WAST file and finally WABT to get the WASM binary. We then show an approach to clone and configure a custom std library headers for Web Assembly to build includes to the standard library.

Compiling C/C++ to WebAssembly using LLVM, Binaryen and WABT

This lesson demonstrates a full build of LLVM roughly following the steps in [GettingStarted.html](http://llvm.org/docs/GettingStarted.html) (or [GettingStartedVS.html](http://llvm.org/docs/GettingStartedVS.html) for Windows), but with the experimental WebAssembly target build option. Prerequisites include cmake (which can be downloaded from [cmake.org/download](https://cmake.org/download/)), Visual Studio on windows, or Xcode command line tools on mac.

Clone and Build LLVM with the Experimental WebAssembly Target

In this lesson we cover the install process for Binaryen (http://github.com/WebAssembly/binaryen) to get the s2wasm binary and WABT (https://github.com/WebAssembly/wabt) to get the wast2wasm binary.

Prerequisites are cmake (https://cmake.org/download/), XCode CLI tools on Mac, or Visual Studio on Windows.

Install Binaryen and the WebAssembly Binary Toolkit (WABT)

We introduce a black-box render function which draws circles to the screen, explaining how the position information is represented in the memory for the renderer (a typed array of [x1, y1, r1, x2, y2, r2, …]). We draw a simple circle (at [0, 0, 100]), then many random circles to get a feel for passing rendering data by directly setting Typed Array memory. The details of the renderer are not discussed at all. We set up some simple dynamics and wall bounds, and then push the circle count up over 1,000,000 renders to demonstrate the performance of dealing with raw memory and WebGL.

Demo repo: https://github.com/guybedford/wasm-demo

_Note the demo is currently only supported in Chrome Canary with the Experimental Web Platform flag (chrome://flags/#enable-experimental-web-platform-feature) enabled due to the use of ES modules and WebGL 2.0._

Typed Arrays in High Performance JavaScript

Using the previous JS example (with some polishing), we start the conversion by copying the JS code into a C file. Step-by-step we run through the principles of converting this JS code into valid C code that we can compile into Web Assembly, based on the same principles we learnt in the initial lessons. We paste the C code into WASM Fiddle to get the resulting WebAssembly binary, and wire it into the application.

Demo repo: https://github.com/guybedford/wasm-demo

_Note the demo is currently only supported in Chrome Canary with the Experimental Web Platform flag (chrome://flags/#enable-experimental-web-platform-feature) enabled due to the use of ES modules and WebGL 2.0._

Step-by-Step JS to WebAssembly Conversion

To compare the performance between JS and WebAssembly, we use an example that calculates the collisions between circles on the screen. This quickly slows down the rendering performance making the performance comparison visible. We briefly go over the same steps of converting JS into C code, and find that the JS version of the code is actually faster than the WASM version - WebAssembly improving performance is not such a simple argument.

Demo repo: https://github.com/guybedford/wasm-demo

_Note the demo is currently only supported in Chrome Canary with the Experimental Web Platform flag (chrome://flags/#enable-experimental-web-platform-feature) enabled due to the use of ES modules and WebGL 2.0._

A First Comparison of the Performance between JS and WebAssembly

To improve the performance of collision detection, we need to dive into the internals of the algorithm. Here we update the JS collision detection code to use a grid for collision detection, which brings a big performance boost at the end.

Demo repo: https://github.com/guybedford/wasm-demo

_Note the demo is currently only supported in Chrome Canary with the Experimental Web Platform flag (chrome://flags/#enable-experimental-web-platform-feature) enabled due to the use of ES modules and WebGL 2.0._

Optimize Collision Detection in JS with a Grid

To write a grid collision detection optimization in C requires thinking about the data structure of the grid more than in JS. In C we can represent this with a linked list and show how to convert the JS optimization code into this structure. When we compare the final performance, the WebAssembly code is now faster than the JS code - being able to write a low-level, more efficient data structure in memory is what gives WebAssembly its best advantage over JS. For those new to the principles, a good introduction to data structures and algorithms is the CLRS Introduction to Algorithms book.

Demo repo: https://github.com/guybedford/wasm-demo

_Note the demo is currently only supported in Chrome Canary with the Experimental Web Platform flag (chrome://flags/#enable-experimental-web-platform-feature) enabled due to the use of ES modules and WebGL 2.0._

Get Started Using WebAssembly (wasm)

Guy Bedford

Course Content

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