For input numbers we should use null instead undefined in toNumber

[stalkerg]

If you return undefined it became the problem for some situations like this (we can't set undefined back):
https://svelte.technology/repl?version=2.30.1&gist=4728f0fd73979c92e7c07ec0a7eebb94

by the standard, the "number input" can contain numbers or empty and empty here is an empty string or null.
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/number

[Conduitry]

I don't know what the problem was supposed to have been when this issue was opened (and I also don't know what version it was against. there is no 2.30.1), but in the latest v2 I don't see anything in the console https://v2.svelte.dev/repl?version=2.16.1&gist=4728f0fd73979c92e7c07ec0a7eebb94

[stalkerg]

@Conduitry
this problem still exists, I can reproduce it even on v3 https://svelte.dev/repl/922cb0532c56400a94d95e8d4536e322?version=3.8.0

please reopen. The main idea is you can't return undefined from "input number" because you can't set it back, it's just not valid by the standard.

[Conduitry]

Returning undefined for an empty number input field happened in #606 as a solution for #584. I don't know what returning null instead would do.

[stalkerg]

I see, anyway return null also should fix #584 and will be consistent with browsers standards.
(and fix browsers warnings)

[stalkerg]

Warnings like this:

VM67:304 The specified value "undefined" is not a valid number. The value must match to the following regular expression: -?(\d+|\d+\.\d+|\.\d+)([eE][-+]?\d+)?

[stalkerg]

@Conduitry did you see the same warning?

[antony]

I see the warning in 3.20.1 - note that the warning doesn't appear in the Svelte console, but the browser console.

[tanhauhau]

Researched on how vue is handling this case,

export function toNumber (val: string): number | string {
  const n = parseFloat(val)
  return isNaN(n) ? val : n
}

https://github.com/vuejs/vue/blob/98b4d683f578bb09c4e56f35048e49441c590a41/src/shared/util.js#L97-L100

we can also set '' as input.value if the value is ''

[Conduitry]

This has been changed to use null instead of undefined in 3.25.0.

[stalkerg]

Thanks!