Web Development with ReasonML

Dangerous Interop

Sometimes you need to convert a JavaScript type to a ReasonML type. For example, one of the reviewers of this book suggested using the Performance^[57] interface for measuring the time required to process the palindrome functions rather than using Js.Date.now as we did. He wrote this code:

miscellanea/misc/src/Identity.re

module Performance = {
  type t; /* DOMHighResTimeStamp - a double, milliseconds since startup */

  [@bs.scope "performance"] [@bs.module "perf_hooks"] 
  external now: unit => t = "";

  external toFloat: t => float = "%identity"; 
  external fromFloat: float => t = "%identity"; 

  let zero: t = fromFloat(0.0);

  let  ...