What is Sledgehammer Bindgen?

Sledgehammer bindgen provides faster rust batched bindings for js code.

How does this compare to wasm-bindgen:

• wasm-bindgen is a lot more general it allows returning values and passing around a lot more different types of values. For most users wasm-bindgen is a better choice. Sledgehammer is specifically designed for web frameworks that want low-level, fast access to the dom.

• You can use sledgehammer bindgen with wasm-bindgen. See the docs and examples for more information.

Why is it fast?

String decoding

• Strings are expensive to decode, but the cost doesn't change much with the size of the string. Wasm-bindgen calls TextDecoder.decode for every string. Sledgehammer only calls TextEncoder.decode once per batch.

• If the string is small, it is faster to decode the string in javascript to avoid the constant overhead of TextDecoder.decode

• See this benchmark: https://jsbench.me/4vl97c05lb/5

String Caching

• You can cache strings in javascript to avoid decoding the same string multiple times.
• If the string is static sledgehammer will hash by pointer instead of by value.

Byte encoded operations

• In sledgehammer every operation is encoded as a sequence of bytes packed into an array. Every operation takes 1 byte plus whatever data is required for it.

• Each operation is encoded in a batch of four as a u32. Getting a number from an array buffer has a high constant cost, but getting a u32 instead of a u8 is not more expensive. Sledgehammer bindgen reads the u32 and then splits it into the 4 individual bytes. It will shuffle and pack the bytes into as few buckets as possible and try to inline reads into js.

• See this benchmark: https://jsbench.me/csl9lfauwi/2