Reducing binary size

Note: More information about reducing binary size can be found in the Rust Wasm Book.

Building in release mode

A common mistake when building a Wasm binary is to forget to build in release mode. If you are using trunk, simply add the --release flag to the build command:

trunk build --release

wee_alloc

wee_alloc is a memory allocator focused on targeting WebAssembly, producing a small .wasm code size, and having a simple, correct implementation. Replacing the default allocator with this one will result in a smaller binary size at the expense of speed and memory overhead.

// Use `wee_alloc` as the global allocator.
#[global_allocator]
static ALLOC: wee_alloc::WeeAlloc = wee_alloc::WeeAlloc::INIT;

Cargo.toml

It is possible to configure release builds to be smaller by using various flags and configurations in your Cargo.toml file.

[profile.release]
# Do not perform backtrace for panic on release builds.
panic = 'abort'
# Perform optimizations on all codegen units.
codegen-units = 1
# Optimize for size.
opt-level = 's' # or 'z' to optimize "aggressively" for size
# Enable link time optimization.
lto = true

wasm-opt

If you are using trunk, add this line to your index.html to enable wasm-opt:

<link data-trunk rel="rust" data-wasm-opt="s" />