I would try optimizing the JS before dropping down to webassembly. For example try replacing let and const with var as let and const in loops have to create a new variable for each iteration.
Have you ever made a for loop using var only to have the variable point to the last value in the iteration ? And had to make a closure using forEach, function or self calling function ? With let you do not have to do that as a new variable is created for each iteration. Instead or reassigned when you use var.
