Function intern

pub fn intern(s: &str) -> &str

Interns Rust strings so that it’s much faster to send them to JS.

Sending strings from Rust to JS is slow, because it has to do a full O(n) copy and also encode from UTF-8 to UTF-16. This must be done every single time a string is sent to JS.

If you are sending the same string multiple times, you can call this intern function, which simply returns its argument unchanged:

intern("foo") // returns "foo"

However, if you enable the "enable-interning" feature for wasm-bindgen, then it will add the string into an internal cache.

When you send that cached string to JS, it will look it up in the cache, which completely avoids the O(n) copy and encoding. This has a significant speed boost (as high as 783%)!

However, there is a small cost to this caching, so you shouldn’t cache every string. Only cache strings which have a high likelihood of being sent to JS multiple times.

Also, keep in mind that this function is a performance hint: it’s not guaranteed that the string will be cached, and the caching strategy might change at any time, so don’t rely upon it.