3 ms·

Which is better `undefinedVar === void 0` or `typeof undefinedVar === 'undefined'`? here says: http://www.2ality.com/2013/04/check-undefined.html http://www.2a

by ttty 12y ago

Which is better `undefinedVar === void 0` or `typeof undefinedVar === 'undefined'`? here says: http://www.2ality.com/2013/04/check-undefined.html http://www.2ality.com/2013/04/check-undefined.html void 0 is safe.

ekmartin 12y ago
I think minifiers use the former because it's shorter, and thus requires less space.
- phpnode 12y ago
  the other benefit is that `void 0` cannot be overwritten in sloppy mode, whereas you can do something crazy like this: undefined = 'lol';
  - evilpie 12y ago
    No you can't. You can do something like function(undefined) {}, but the global 'undefined' is non-writable and non-configurable.
    - ahoge 12y ago
      That's an ES5 change. With ES3, you can overwrite NaN, Infinity, and undefined.
      - LunaSea 12y ago
        Only in strict mode I though no ?
        ahoge 12y ago
        Generally. Technically, it's a "breaking change". As you can imagine, this didn't actually affect anyone.
kibibu 12y ago
I was curious too, so here's a jsPerf: http://jsperf.com/check-for-undefined-argument http://jsperf.com/check-for-undefined-argument On Chrome 35, looks like comparing to void 0 is a bit faster. Would love some more samples though.