The isFinite() type declaration doesn't specify the right type

[SetTrend]

⚙ Compilation target

esnext

⚙ Library

The VS Code built in library

Missing / Incorrect Definition

/**
 * Determines whether a supplied number is finite.
 * @param number Any numeric value.
 */
declare function isFinite(number: number): boolean;

should be:

declare function isFinite(number: any): boolean;

Sample Code

isFinite("123");   // number as string yields true

Documentation Link

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isFinite#difference_between_number.isfinite_and_global_isfinite

[MartinJohns]

This is intentional. Duplicate of #4002.

[RyanCavanaugh]

https://github.com/Microsoft/TypeScript/wiki/FAQ#numberisfinite-and-numberisnan-are-typed-correctly

[SetTrend]

That's odd … This explanation contradicts the description from MDN, which suggests using the global function for type conversion.

Apparently, many people fall through this traphole.

Wouldn't it make sense to add a link to https://github.com/Microsoft/TypeScript/wiki/FAQ#numberisfinite-and-numberisnan-are-typed-correctly in the lib? For example:

/**
 * Determines whether a supplied number is finite.
 * @param number Any numeric value.
 * @description The parameter data type is `number` by intention.
 * @see https://github.com/Microsoft/TypeScript/wiki/FAQ#numberisfinite-and-numberisnan-are-typed-correctly
 */
declare function isFinite(number: number): boolean;

This could reduce the confusion.

[RyanCavanaugh]

100% of the lib typing is there intentionally, I don't know why this one deserves a different call-out.

MDN in fact warns against using this when a coercion may occur:

The isFinite() function determines whether a value is finite, first converting the value to a number if necessary. A finite number is one that's not NaN or ±Infinity. Because coercion inside the isFinite() function can be surprising, you may prefer to use Number.isFinite().

[SetTrend]

I see … Nonetheless, MDN claims that coercion is taking place and expected behavior for isFinite().

There is a well-known comprehensive type documentation on JavaScript on MDN, but there's none on TypeScript. I don't know the numbers, but I would expect millions of users to consult the MDN documentation on isFinite(). Wouldn't you agree it would be sensible to consider these million users in the JsDoc documentation rather then expecting them to refer to a less known, well, exotic, Wiki?