Fix issue with IsNumeric when input is whitespace

[bconnorwhite]

I'm not actually sure if this is a bug or not, but it at least seems confusing. (Feel free to close if this is expected behavior).

Currently IsNumeric passes with whitespace:

IsNumeric<" ">; // true
IsNumeric<" \t\n\r\f\v">; // true

Instead I've just added a check to ensure that if the type extends `${number}`, it isn't purely whitespace.

[sindresorhus]

I agree it's a bug, but I'm not sure the proposed solution is correct. This kinda feels like a TypeScript bug. Maybe worth opening an issue there first?

A fix for this will also need to come with some tests.

[bconnorwhite]

It sounds like this is intended, here is an issue in the TypeScript repo: microsoft/TypeScript#46109

They're trying to match the behavior of Number("string") such that anything that doesn't resolve to NaN or +/-Infinity is considered valid.

This seems less useful given the intent of this library though. As an example, when designing types for string casing conversions, the distinction between spaces/numbers/etc. is important to know where to split a string into words

[bconnorwhite]

As a side note, because SplitWords parses one character at a time I don't think this actually causes any issues, but "1e2" also passes IsNumeric. There are probably three useful types here:

• IsNumeric - does the string pass Number()?
• IsNumber - IsNumeric, but after trimming spaces first
• IsDigit - Only allow 0-9

Right now only SplitWords is using IsNumeric though, so maybe not worth adding these types

[sindresorhus]

It sounds like this is intended, here is an issue in the TypeScript repo: microsoft/TypeScript#46109

I don't think you read the whole thread because the last comment says it's something they want to fix: microsoft/TypeScript#46109 (comment)

[sindresorhus]

Can you add a comment that says this is a workaround for microsoft/TypeScript#46109 (comment) ?

[sindresorhus]

Super nitpicky, but I prefer the modern escape syntax: \u{7A}.

https://exploringjs.com/es6/ch_unicode.html#sec_escape-sequences

[sindresorhus]

IsNumeric - does the string pass Number()?

I don't think the Number behavior is useful. So we should just fix isNumeric.

IsDigit - Only allow 0-9

Could be a useful type, but beyond the scope of this pull request. Should be called IsASCIIDigit as IsDigit would be assumed to include all Unicode digits.

[bconnorwhite]

Updated the escape formats.

Also realized that we need to use Trim, otherwise something like this passes:

IsNumeric<" 1 ">

Trim isn't currently accounting for all whitespace characters, so I updated Trim to use the new Whitespace type in internal.d.ts, which should also more accurately match String.prototype.trim.