TLDR; Everyone lied to you when they said let and const don't create global variables. They absolutely do .. it's just that they don't create window. global variables. More on reddit.com

The number one thing I've seen writing performant JavaScript code has been making sure that things stay as unboxed primitives (ints, double, etc). Preferably in large typed arrays. Chances are your function itself isn't that hot, I bet the loop is though. Declare primitives once at the top of the function an they'll get allocated on the stack and incur zero GC. (Unless you do something like myInt["someProp"] = "something", in which case it's boxed and slow) More on reddit.com

Setting the color in the handler is an anti-pattern in Vue. Instead, you should use a computed property based on the errors prop. In this way you will separate the business logic from the representation. More on reddit.com

You don't need `let` or `var` since you're inside a class definition. Anything you write there is part of the class. So just define the variables if you want (or you can just set them in constructor, they don't need to be predefined). The problem with outputting is that you're accessing `name` which isn't the same as `this.name`. If you run your code in Node.js it'll even say "name is not defined." Using `console.log(this.name + "crunch")` will do what you want. You have to access the class variable, not just any `name` that happens to be in the context. More on reddit.com