> Aren't most JS engines able to do this optimization regardless of |0 Yes - if you are taking 'after every math operation' literally. JavaScript engines (and

> Aren't most JS engines able to do this optimization regardless of |0 Yes - if you are taking 'after every math operation' literally. JavaScript engines (and other dynamic language engines - nothing special about JavaScript) track types at a finger-grained level than simple generic 'number' or not. They already know if a number is a guaranteed integer, and even in some cases which bits can be set in that number. Sometimes the compiler doesn't want to prove more advanced properties like range when for example a value escapes, due to the overhead of tracking this, and then it's useful to do the trick in this article. Here's a worked example in a Ruby compiler for example https://chrisseaton.com/truffleruby/stamping-out-overflow-checks/ https://chrisseaton.com/truffleruby/stamping-out-overflow-ch.... But the author knows infinitely more than me about JavaScript compilation - they're ex-Google and Meta, including working on both Chromium and WebKit. They could show their working by for example showing some compiler IR for the engines they know about.