Hacker News Reader

Comment by HWR_14 | Hacker News Reader

> I wonder how many jobs they’ve applied to while bragging about their millions of monthly NPM downloads.

isEven claims to be a learning project. It depends on isOdd and isNumber, both of which were admitted (IIRC) to be explicit NPM download boosting projects. Such that the author of isOdd added it to major modules whenever they could

View on HN

isNumber would make for a legit package. Is there a good way in javascript to determine confidently if an arbitrary input is a number?

e.g: [1, "one", true, false, 0, "zero", null, undefined]

edit: also ["1", "0", etc]

edit 2: also [NaN]

  “number" == typeof variable

Works for decimals, too.

Although maybe you meant to include

"1"

In your examples?

Unfortunately "not a number" is typeof "number"

    "number" === typeof NaN

Returns true.

That's a tricky one that I think would depend on use case. Yes, of course NaN isn't a number, but it's still kind of a number, depending on context.

NaN is a float according to IEEE754. All numbers in Javascript being floats, it makes sense that typeof NaN === "number".

Now, the fact that IEEE754 is insane is something else, but JS does nothing wrong (aside from not having not-floats)

> Now, the fact that IEEE754 is insane is something else, but JS does nothing wrong (aside from not having not-floats)

JS has BigInt - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...

BigInt is relatively recent, all things considered. JS only having floats is a conception flaw.

I mean, it depends on context what “numbers” are acceptable. For an overly general solution:

  const allowNumbers = {
    all: () => true,
    notNaN: n => !Number.isNaN(n),
    finite: Number.isFinite,
    integer: Number.isInteger,
    smol: n => Math.abs(n) < Number.EPSILON,
    lorge: n => n > Number.MAX_SAFE_INTEGER || n < Number.MIN_SAFE_INTEGER,
  }

  function isNumber(n, allow = allowNumbers.all) {
    return ("number" === typeof n) && allow(n);
  }

This isn't bad, but for maintainability, it should be split into at least nine packages.

In the type of things that Javascript considers 'numbers', it's a value used to indicate that it's not of the type of things that math considers 'numbers'.

... typeof foo === 'number'

typeof x === 'number' && !Number.isNaN(x)

This seems like the best solution.

Any weird edge cases against this one?

+/- Infinity, better to use Number.isFinite.

Infinities.

Comparing it against the list of examples given in is-number, this solution does not properly handle numbers represented as strings, and it also recognizes Infinity as a number.

Because strings aren't numbers and Infinity is a number

Strings are the safest way to hold big numbers in JavaScript due to how JavaScript represents numbers. Also no, infinity is not a number. It's a concept.

Numbers is a concept. For some purposes it is useful to consider a number that is infinite, which is why concepts like the extended real number line have been invented.

    typeof v === "number"

The rest is parsing territory.

Looks like the author of these packages agrees. While the is-even and is-odd packages are under the i-voted-for-trump user with the description "This is a joke", the is-number package [1] is still kept under the main profile of the author, the repository is still active on GitHub and there are active issues.

[1] https://github.com/jonschlinkert/is-number

Number.isFinite() does very well in most cases

that is odd

Reply on news.ycombinator.com