[txttran]

From: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...

['1', '2', '3'].map(parseInt); // While one could expect [1, 2, 3] // The actual result is [1, NaN, NaN]

parseInt is often used with one argument, but takes two. The first is an expression and the second is the radix. To the callback function, Array.prototype.map passes 3 arguments: the element, the index, the array. The third argument is ignored by parseInt, but not the second one, hence the possible confusion.

[crimsonalucard]

This shows how badly javascript was designed. Functions when used improperly should throw an exception not "sort of work."

[reificator]

To take up the mantle of Devil's Advocate:

Neither of these are doing anything wrong on their own[1]. When you go to map something you want to be able to access the index sometimes. When you parse an int, you sometimes want to be able to specify a base. Maybe in a strongly typed language you might use an enum with valid bases instead of an int, but that doesn't make sense in a dynamically typed language[2]. Maybe you use different function names if you want to parse an int in decimal vs an arbitrary base, I can't argue with that, but overloaded functions/methods are the norm and not the exception in most languages I've used.

[1]: Except parseInt's default radix which is ambiguous and the cause of countless bugs. But this bug is because we ARE specifying it.

[2]: And no, being dynamically typed is not inherently bad design.

[crimsonalucard]

In terms of design I'm talking about an exception not the arity of the function. A hidden NaN in an array of numbers is like a javascript promise for an error in the future. This isn't IO so it's better to kill it now rather than killing it sometime in the future.

Actually, to be honest will NaN even launch an exception? Does 1 + NaN cause an exception or does it propagate more NaNs all over the code?

Imagine you are debugging a 10000 line function that's suppose to return an int, but instead returns a NaN. Where did this error occur in the 10000 lines? Sure, I can say all kinds of stuff to make finding this error sound simple but if exceptions were thrown instead of assigning NaNs to some variable life would be easier. The exception would tell me the exact line of the illegal operation while a NaN tells me nothing.

Javascript treats the "NaN" type as if it's a number... in the sense that when you do a math operation on something that is a NaN you get another NaN... The reality is... the very abbreviation "NaN" stands for is "Not a Number" so the addition of a number and something that is not a number should not even occur. Seriously? They should have called it "LoL" or "WtF" because these are more appropriate abbreviations.

[reificator]

> Imagine you are debugging a 10000 line function that's suppose to return an int, but instead returns a NaN.

I'm imagining that. It's my first day at a new job cleaning up a legacy codebase, but upon opening up a single 10kloc function written in JS, I realize that I made a terrible mistake and immediately hand in my resignation.

In the meantime, I set a breakpoint at the end of the function, inspect the inline value annotations for NaNs, and trace them back to the start.

Relative to any other debugging task in a 10kloc function, that doesn't sound bad at all. If it's consistently returning NaN, that should take maybe half an hour.

Also, I'd be really surprised if the function was made to return an int, because JS doesn't have integer datatypes.

[crimsonalucard]

Read what I wrote again:

> Sure, I can say all kinds of stuff to make finding this error sound simple but if exceptions were thrown instead of assigning NaNs to some variable life would be easier.

I said this in the parent post and sure enough the reply is exactly inline with what I said was going to happen. I don't hate javascript, but it has its horrible horrible warts.

>Relative to any other debugging task in a 10kloc function, that doesn't sound bad at all. If it's consistently returning NaN, that should take maybe half an hour.

An exception would take a second. An exception would give you the target line of every illegal operation; while a NaN propagates itself like a virus along every arithmetic operation.

Some people find it easy to run a 20 miles, sure but that still doesn't change the fact that cars are much better. Get the analogy? You are running 20 miles and telling me how you don't mind... I'm saying sure, but driving still has a purpose in life.

[reificator]

> I said this in the parent post and sure enough someone who is a fan of javascript had to reply with exactly what I said was going to happen.

Breakpoints are off the table? Seriously? I didn't realizing using a debugger made me a JS fanboy.

Wrapping all of your basic arithmetic in try/catch blocks is completely unreasonable. If you need to check for NaN, check for NaN. Making arithmetic substantially slower in the general case to catch the uncommon cases is exactly the problem NaN was introduced to solve.

[reificator]

Look, misattributing the introduction of NaN to JS is not going to help make the case that JS is poorly designed[1].

JS uses double-precision floating point numbers, based on the IEEE 754 standard first published in 1985.

[1]: Though there is a case that using doubles for all numbers is poor design, that's a different topic altogether.

[crimsonalucard]

I don't know where NaNs were introduced, but I never attributed the introduction of NaNs to javascript. If JS is just propagating a bad design, it still fits the description of being poorly designed.

Not to mention a null. null + 1 = 1. This is even worse. Your 1000loc function returns a legit number but it's a little bit off... and you have to find it. Imagine never having to have to do that with a language like python... 1+None and 1/0 all return named exceptions with line numbers in python.

[reificator]

No, not following the globally agreed upon standard for the sole purpose of making arithmetic slower in the general case would be bad design.

[dragonwriter]

It makes sense to have a function that is like the common functional “map” but passing the index as well, it's probably not a great design to have it be called “map” and have the basic, no-index behavior rely on the passed function taking only one arg, especially in a language where functions that usually take one arg but also have optional args are common.