Building to WebAssembly (WASM) ============================= {{#include ../../links.md}} It is possible to use Rhai when compiling to WebAssembly (WASM). This yields a scripting engine (and language) that can be run in a standard web browser. Why you would want to is another matter... as there is already a nice, fast, complete scripting language for the the common WASM environment (i.e. a browser) - and it is called JavaScript. But anyhow, do it because you _can_! When building for WASM, certain features will not be available, such as the script file API's and loading modules from external script files. Size ---- Also look into [minimal builds] to reduce generated WASM size. As of this version, a typical, full-featured Rhai scripting engine compiles to a single WASM file less than 200KB gzipped. When excluding features that are marginal in WASM environment, the gzipped payload can be further shrunk to 160KB. Speed ----- In benchmark tests, a WASM build runs scripts roughly 1.7-2.2x slower than a native optimized release build. Common Features --------------- Some Rhai functionalities are not necessary in a WASM environment, so the following features are typically used for a WASM build: | Feature | Description | | :-----------: | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | [`unchecked`] | When a WASM module panics, it doesn't crash the entire web app; however this also disables [maximum number of operations] and [progress] tracking so a script can still run indefinitely - the web app must terminate it itself. | | [`only_i32`] | JavaScript has only one `number` type and we're only supporting `wasm32` here (so far). | | [`no_module`] | A WASM module cannot load modules from the file system, so usually this is not needed, but the savings are minimal; alternatively, a custom [module resolver] can be provided that loads other Rhai scripts. | The following features are typically _not_ used because they don't make sense in a WASM build: | Feature | Why unnecessary | | :-----------: | ------------------------------------------------------------------ | | [`sync`] | WASM is single-threaded. | | [`no_std`] | `std` lib works fine with WASM. | | [`internals`] | WASM usually doesn't need to access Rhai internal data structures. |