Comment by Goofy_Coyote | Hacker News Reader

Comment by Goofy_Coyote | Hacker News Reader

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Need some help understanding what’s going on here.

In

  function example(measurement) {
    console.log(calculation); // undefined - accessible! calculation leaked out
    console.log(i); // undefined - accessible! i leaked out
  <snip>

Why does the author say `calculation` and `i` are leaking? They’re not even defined at that point (they come later in the code), and we’re seeing “undefined” which, correct me if I’m wrong, is the JS way of saying “I have no idea what this thing is”. So where’s the leakage?

Two spaces before each line in the code block. HN doesn't use markdown, it's easy to do even on mobile, a demonstration:

  function example(measurement) {
    console.log(calculation); // undefined - accessible! calculation leaked out
    console.log(i); // undefined - accessible! i leaked out <snip>

It's "leaking" because the variable is in scope, it's associated value is "undefined". This is different than with let/const where the variable would not be in scope at that point in the function. An undefined value bound to a variable is not the same as "I have no idea what this thing is". That would be the reference errors seen with let/const.

Thanks for the tip, and also thanks for the explanation. I understand what’s going on here now. Much appreciated

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