Why is 'for(var item in list)' with arrays considered bad practice in JavaScript?

Question

Given a simple zero based, numerically indexed array:

var list = [\'Foo\', \'Bar\', \'Baz\'];

Many times, I have noticed that when someone

Answer 1

for ... in ... doesn't return items of list, but instead enumerates array properties.

For that reason alone, it cannot act as a replacement of for (i=0; i loop.

The appropriate alternative is for ... of ... construct. It enumerates values of an iterable object, such as an array. You can read more about it on MDN Web Docs: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...of

It's supported by the relevant modern browsers (Internet Explorer doesn't count, with it being replaced by Microsoft Edge). If you can afford not supporting older browsers, it's probably the way to go. You can check the convenient browser support table at the end of aforelinked MDN page to see which browser versions actually allow for ... of ... usage.