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Comment by horsawlarway | Hacker News Reader

That's because default params in JS are essentially syntactic sugar ex -

  function example(a = 1) {
  ...
  }

behaves the same as

  function example(a) {
  a = (typeof a !== 'undefined') ?  a : 1
  ...
  }

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Which also means the suggestion to use ?? has a different result then using a default param. ?? will catch both null and undefined, where as a default parameter will only trigger on undefined.

?? catches any falsy value, so it is quite semantically different than default arguments, and also quite different from ||

Did you write that backwards? || checks for falsy, ?? checks for null/undefined

Yup, you're absolutely correct. Null is considered a valid value for a default param.

  function test(a = 1) {
    console.log(a)
  }

  test() // -> 1 is printed
  test(null) // -> null is printed
  test(undefined) // -> 1 is printed

Not because.

You could have sugar evaluated once, sugar evaluated each time, not-sugar evaluated once, or not-sugar evaluated each time.

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