Why does parseInt(1/0, 19) return 18?

http://stackoverflow.com/questions/11340673/why-does-parseint1-0-19-return-18

by onemach • 14 years ago

55 66 14 years ago

stackoverflow.com

MrEnigma• 14 years ago

If this was in PHP people would be crying out what a bad and horrible language it is.

Javascript it's seen as an amusing conundrum.

JoeCortopassi2• 14 years ago

The only reason something like this makes it to the front page, is because of the popularity of things like node.js right now. This is a bug, not a feature.

JonoW2• 14 years ago

The crazy part is that it's not a bug; it's behaving exactly as it's specified to.

chris_wot12• 14 years ago

No, no it's not. It's actually part of ECMA-262.

Javascript allows numbers to be a number, NaN or positive/negative infinity. It is well specified within the spec that "Division of a nonzero finite value by a zero results in a signed infinity. The sign is determined by the rule already stated above." [1]

Before you get your knickers in a twist, this is compliant with IEEE 754; although the IEEE define it as an exception.

1. ECMA-262, pg 74, "11.5.2 Applying the / Operator"

asto2• 14 years ago

The reason javascript won't get nearly as much ridicule as PHP is because there's no other choice with javascript. Most arguments against PHP are in the form - I'm using <super awesome language> because PHP has .... faults.

Also, the fact that very few people code pure javascript, instead choosing frameworks like jquery, goes to show how much people like it!

philwelch• 14 years ago

> Also, the fact that very few people code pure javascript, instead choosing frameworks like jquery, goes to show how much people like it!

I'd say most languages are coded in frameworks and not just the "pure" language.

jpk2• 14 years ago

I second this. Javascript is a dumpster-fire of a language, as is PHP. If I could use anything other than javascript for scripting in the browser, I would, but I can't. So I use it. I can use things other than php on the server, so I do.

However, I'd say the use of libraries and frameworks help javascript programmers, for sure, but that doesn't make the language any less of a mess (and in some cases, like jQuery setting "this" to whatever the hell it wants, makes it more of a mess). I can't speak for php, because I've used it far less, but I suspect the same holds true there, too.

maggit3• 14 years ago

Sorry, your point about jQuery is off the mark. jQuery is a library (not a framework), and if you are not using libraries you are most likely doing it wrong, in any language!

jQuery does nothing to alter the language, so people using it are still coding pure JavaScript. jQuery itself is implemented in pure JavaScript.

----

There does exist variants of JavaScript, such as Paper.js, Protovis and maybe even CoffeScript, but these are not what the majority of JavaScript users use.

bentlegen• 14 years ago

The reality is that nobody writes parseInt(1/0, 19). Get off your high horse.

LBarret2• 14 years ago

it is just an example, but it shows the kind of danger/potential bugs comes with using a badly designed language.

PS : I know it had been designed in 11 days and as such it is an achievement, but as the most used programming language it is quite awful.

batista2• 14 years ago

The reality is that flaws like that are seldom skin deep, and can bite you in other parts of the language, even where you don't expect them.

Lack of type safety in a dynamic language is one thing, but awful type coercion is a different beast altogether.

Lazare• 14 years ago

First, Javascript isn't nearly as bad as PHP. Second, even the biggest fans of Javascript recognize its problems (the same can't be said of PHP). Third, even the biggest decractors of Javascript recognize its one overwhelming strength: It's the only language to run in the browser.

steve-howard• 14 years ago

Remember that the main reason PHP has such a broad user base is that it runs with fairly comparatively little setup on every server out there. That doesn't make it good. JavaScript is the only language to run in the browser because years ago someone developed it for that purpose. We could be using Python or Ruby or Brainfuck if there were any way to convince all major browser vendors to support that directly.

chris_wot12• 14 years ago

I know! In PHP, try the equivalent:

  print intval(NaN, 19);

Result in PHP 5.2.17 is:

Clearly, that is correct.

PHP does the following:

  intval('42', 8); // => 34
  intval(42, 8);   // => 42

Now try:

  print intval(strval("19.99"*100));
  print "<br>";
  print intval("19.99"*100);

This returns:

  1999
  1998

saurik6• 14 years ago

That is not equivalent: 1/0 returns +Inf, not NaN. In JavaScript, parseInt(NaN, 19) actually returns NaN, as there are no valid digits below radix 19 in the string "NaN". PHP, in fact, has the same behavior that JavaScript does: if you do parseInt or intval on (NaN, 24) you will get 13511 (23 * 24 * 24 + 10 * 24 + 23) in either language.

Unrelated, it seems like intval(1/0, 19) in PHP also returns 0 because 1) intval returns 0 if given an empty string (JavaScript's parseInt returns NaN if given an empty string) and 2) 1/0 seems to return something hilarious... it converts to "", but gettype() on it returns "boolean"... I sadly don't know PHP well enough to understand what it is ;P.

LBarret2• 14 years ago

Please put Python or Ruby or X in the browser.

Javascript is no better than PHP. It is there - like Php in its time- because we have no other choice.

We're supposed to be professionals and one of our main tool is a joke.

saraid2162• 14 years ago

No one is stopping you from rolling your own browser and taking market share away from the current Big Three.

Or from forking Chrome, since it's open source, and then offering your patch back to the central repo. Not sure if Firefox is open source, but could use that instead, too, if it is.

icebraining• 14 years ago

Firefox is not only open source, as it's developed mostly by the community, in cooperation with a non-profit foundation (Mozilla), whose mission is to keep the Internet open and free for everyone to participate.

Chrome is a closed source browser based on the open source Chromium, and it includes some features that the open version doesn't, like embedded PDF reader or MP3 support.

chris_wot12• 14 years ago

Nobody would use it as it wouldn't have market share. But that's besides the point. The behaviour is actually well defined; the only issue is with parseInt() taking the first character it sees as a number, converting it from it's base to base 10 and then prints the number. The issue being, of course, is that it would have been more sensible to given an exception for non-numeric strings.

tikhonj2• 14 years ago

Python also has plenty of stupid edge cases while being less functional, flexible but more complex than JavaScript. My theory is that Python gets good press because nobody has to use Python, so the people who don't like it just use a different language instead of complaining. Obviously, this does not hold for JavaScript.

If you're going to complain about language choices, don't force everybody on Python!

I can't comment on Ruby because I have never had to use it.

What would be perfect is Scheme in the browser. And, apparently, we almost had it except marketing or management forced Eich to make it look like Java resulting in JavaScript.

chris_wot12• 14 years ago

Ah! Nice work - that makes total sense.

Incidentally, PHP doesn't have the concept of positive or negative Infinity, just NaN. However, when I tried:

  print inval(1/0);

I got an exception. But point taken :-)

Edit: I might not be correct about positive or negative infinity in PHP... apologies if I have at all mislead anyone!

Also: got a proxy error, so this got reposted, then I deleted one of the posts, but the other post got marked deleted. So third post about this!

saurik6• 14 years ago

Please read my comment below regarding this behavior in PHP. In addition, I will add that 1/0 here is not returning NaN (if you attempt to print it as a string you won't get "NaN"), and intval itself actually has the same behavior as JavaScript. (edit: Oh, I just realized the other comment I replied to was also you. ;P)

chris_wot12• 14 years ago

Argh! Sorry, proxy error caused all sorts of problems :(

jaimebuelta• 14 years ago

Am I the only one that has laugh maniacally after reading this? X-D

mattdeboard2• 14 years ago

Contrary to what some people may think, this is non-obvious & surprising behavior which has nothing to do with JS being a "dynamic language". It requires knowing that the IEEE floating point standard arbitrarily defines 1/0 as positive infinity instead of being (the more widely accepted, obvious and unsurprising) undefined value. I believe JS is a powerful language but calling this reasonable behavior smacks of Stockholm Syndrome.

lifthrasiir2• 14 years ago

It is mainly related to the fact that parseInt in JS slightly converts a positive infinity to a string "Infinity". Base 19 does not add anything to the humor. And well, neither does the presence of a positive infinity itself.

So yes, this is nothing to do with JS being a dynamic language (which main feature is not a variable/slot but a value having a type), but it's something to do with it being a weakly typed language (which main feature is an implicit and generally unpredictable type conversion). Of course many popular dynamic languages are still strongly typed in this sense.

ibotty2• 14 years ago

that js implements the floating point standard is not js' fault. but that parse("1something unreasonable", 2) == 1 is just wrong. it should generate an exception.

esbwhat• 14 years ago

this wouldn't actually solve the problem for base 36, though.

lucian19003• 14 years ago

I would say the (bigger) problem is in JavaScript randomly calling toString on things, especially when you're calling parseInt on a number already.

VMG• 14 years ago

Generally type coercion seems like a bad idea in most languages

chris_wot12• 14 years ago

It's not arbitrary, in fact the IEEE give their reasons in a FAQ [1].

1. http://grouper.ieee.org/groups/754/faq.html#exceptions

Why does parseInt(1/0, 19) return 18?

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