The big thing that makes javascript slow (that the optimizer can’t really fix) is complex data structures.
For example, if you want to implement an editable string, you have to do so using an array of smaller strings and hope the optimizer can figure it out, or slice() and re-join a single “immutable” string. Either way, your javascript code will be slower than the C/rust equivalent because the language is less expressive. Javascript has the same problem with b-trees, skip lists, ropes, gap buffers, AABB trees, and so on. You can implement all of this stuff in javascript - you just end up with much more memory indirection than you want. And for trees with different internal nodes and leaves, your code will give the optimizer indigestion.
In my experience, basically any of these data structures will run about 10-200x slower than their native counterparts. (If both are well optimized). To me this is the big performance advantage wasm has - that we can make high performance data structures.
I’m working on a CRDT in Rust. The fastest JS implementation I know of takes about 1 second to replay an editing trace from a user. In rust I can replay the same trace in 0.01 seconds (100x faster), by using a skip list. In wasm I can do it in about 0.03 seconds.
For example, if you want to implement an editable string, you have to do so using an array of smaller strings and hope the optimizer can figure it out, or slice() and re-join a single “immutable” string. Either way, your javascript code will be slower than the C/rust equivalent because the language is less expressive. Javascript has the same problem with b-trees, skip lists, ropes, gap buffers, AABB trees, and so on. You can implement all of this stuff in javascript - you just end up with much more memory indirection than you want. And for trees with different internal nodes and leaves, your code will give the optimizer indigestion.
In my experience, basically any of these data structures will run about 10-200x slower than their native counterparts. (If both are well optimized). To me this is the big performance advantage wasm has - that we can make high performance data structures.
I’m working on a CRDT in Rust. The fastest JS implementation I know of takes about 1 second to replay an editing trace from a user. In rust I can replay the same trace in 0.01 seconds (100x faster), by using a skip list. In wasm I can do it in about 0.03 seconds.